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Gaussian integer - Wikipedia
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class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Euclidean division</span> </div> </a> <ul id="toc-Euclidean_division-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Principal_ideals" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Principal_ideals"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Principal ideals</span> </div> </a> <ul id="toc-Principal_ideals-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Gaussian_primes" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Gaussian_primes"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Gaussian primes</span> </div> </a> <ul id="toc-Gaussian_primes-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Unique_factorization" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Unique_factorization"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Unique factorization</span> </div> </a> <ul id="toc-Unique_factorization-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Gaussian_rationals" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Gaussian_rationals"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Gaussian rationals</span> </div> </a> <ul id="toc-Gaussian_rationals-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Greatest_common_divisor" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Greatest_common_divisor"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>Greatest common divisor</span> </div> </a> <ul id="toc-Greatest_common_divisor-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Congruences_and_residue_classes" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Congruences_and_residue_classes"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>Congruences and residue classes</span> </div> </a> <button aria-controls="toc-Congruences_and_residue_classes-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Congruences and residue classes subsection</span> </button> <ul id="toc-Congruences_and_residue_classes-sublist" class="vector-toc-list"> <li id="toc-Examples" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Examples"> <div class="vector-toc-text"> <span class="vector-toc-numb">8.1</span> <span>Examples</span> </div> </a> <ul id="toc-Examples-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Describing_residue_classes" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Describing_residue_classes"> <div class="vector-toc-text"> <span class="vector-toc-numb">8.2</span> <span>Describing residue classes</span> </div> </a> <ul id="toc-Describing_residue_classes-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Residue_class_fields" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Residue_class_fields"> <div class="vector-toc-text"> <span class="vector-toc-numb">8.3</span> <span>Residue class fields</span> </div> </a> <ul id="toc-Residue_class_fields-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Primitive_residue_class_group_and_Euler's_totient_function" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Primitive_residue_class_group_and_Euler's_totient_function"> <div class="vector-toc-text"> <span class="vector-toc-numb">9</span> <span>Primitive residue class group and Euler's totient function</span> </div> </a> <ul id="toc-Primitive_residue_class_group_and_Euler's_totient_function-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Historical_background" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Historical_background"> <div class="vector-toc-text"> <span class="vector-toc-numb">10</span> <span>Historical background</span> </div> </a> <ul id="toc-Historical_background-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Unsolved_problems" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Unsolved_problems"> <div class="vector-toc-text"> <span class="vector-toc-numb">11</span> <span>Unsolved problems</span> </div> </a> <ul id="toc-Unsolved_problems-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">12</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Notes" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Notes"> <div class="vector-toc-text"> <span class="vector-toc-numb">13</span> <span>Notes</span> </div> </a> <ul id="toc-Notes-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">14</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">15</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Gaussian integer</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 31 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-31" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">31 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%B9%D8%AF%D8%AF_%D8%B5%D8%AD%D9%8A%D8%AD_%D8%BA%D8%A7%D9%88%D8%B3%D9%8A" title="عدد صحيح غاوسي – Arabic" lang="ar" hreflang="ar" data-title="عدد صحيح غاوسي" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/%D0%93%D0%B0%D1%83%D1%81%D0%B0%D0%B2%D1%8B_%D1%86%D1%8D%D0%BB%D1%8B%D1%8F_%D0%BB%D1%96%D0%BA%D1%96" title="Гаусавы цэлыя лікі – Belarusian" lang="be" hreflang="be" data-title="Гаусавы цэлыя лікі" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target"><span>Беларуская</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Enter_de_Gauss" title="Enter de Gauss – Catalan" lang="ca" hreflang="ca" data-title="Enter de Gauss" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cv mw-list-item"><a href="https://cv.wikipedia.org/wiki/%D0%93%D0%B0%D1%83%D1%81%D1%81_%D1%82%D1%83%D0%BB%D0%BB%D0%B8_%D1%85%D0%B8%D1%81%D0%B5%D0%BF%C4%95%D1%81%D0%B5%D0%BC" title="Гаусс тулли хисепĕсем – Chuvash" lang="cv" hreflang="cv" data-title="Гаусс тулли хисепĕсем" data-language-autonym="Чӑвашла" data-language-local-name="Chuvash" class="interlanguage-link-target"><span>Чӑвашла</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Gaussovo_cel%C3%A9_%C4%8D%C3%ADslo" title="Gaussovo celé číslo – Czech" lang="cs" hreflang="cs" data-title="Gaussovo celé číslo" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Gau%C3%9Fsche_Zahl" title="Gaußsche Zahl – German" lang="de" hreflang="de" data-title="Gaußsche Zahl" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Entero_gaussiano" title="Entero gaussiano – Spanish" lang="es" hreflang="es" data-title="Entero gaussiano" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Ga%C5%ADsa_entjero" title="Gaŭsa entjero – Esperanto" lang="eo" hreflang="eo" data-title="Gaŭsa entjero" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%B9%D8%AF%D8%AF_%D8%B5%D8%AD%DB%8C%D8%AD_%DA%AF%D8%A7%D9%88%D8%B3%DB%8C" title="عدد صحیح گاوسی – Persian" lang="fa" hreflang="fa" data-title="عدد صحیح گاوسی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Entier_de_Gauss" title="Entier de Gauss – French" lang="fr" hreflang="fr" data-title="Entier de Gauss" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Enteiro_de_Gauss" title="Enteiro de Gauss – Galician" lang="gl" hreflang="gl" data-title="Enteiro de Gauss" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EA%B0%80%EC%9A%B0%EC%8A%A4_%EC%A0%95%EC%88%98" title="가우스 정수 – Korean" lang="ko" hreflang="ko" data-title="가우스 정수" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%97%E0%A4%BE%E0%A4%8A%E0%A4%B8%E0%A5%80_%E0%A4%AA%E0%A5%82%E0%A4%B0%E0%A5%8D%E0%A4%A3%E0%A4%BE%E0%A4%82%E0%A4%95" title="गाऊसी पूर्णांक – Hindi" lang="hi" hreflang="hi" data-title="गाऊसी पूर्णांक" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Intero_di_Gauss" title="Intero di Gauss – Italian" lang="it" hreflang="it" data-title="Intero di Gauss" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%97%D7%95%D7%92_%D7%94%D7%A9%D7%9C%D7%9E%D7%99%D7%9D_%D7%A9%D7%9C_%D7%92%D7%90%D7%95%D7%A1" title="חוג השלמים של גאוס – Hebrew" lang="he" hreflang="he" data-title="חוג השלמים של גאוס" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-kk mw-list-item"><a href="https://kk.wikipedia.org/wiki/%D0%93%D0%B0%D1%83%D1%81%D1%81_%D1%81%D0%B0%D0%BD%D1%8B" title="Гаусс саны – Kazakh" lang="kk" hreflang="kk" data-title="Гаусс саны" data-language-autonym="Қазақша" data-language-local-name="Kazakh" class="interlanguage-link-target"><span>Қазақша</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/Gauss-eg%C3%A9sz" title="Gauss-egész – Hungarian" lang="hu" hreflang="hu" data-title="Gauss-egész" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%97%E0%B5%8B%E0%B4%B8%E0%B4%BF%E0%B4%AF%E0%B5%BB_%E0%B4%AA%E0%B5%82%E0%B5%BC%E0%B4%A3%E0%B5%8D%E0%B4%A3%E0%B4%B8%E0%B4%82%E0%B4%96%E0%B5%8D%E0%B4%AF" title="ഗോസിയൻ പൂർണ്ണസംഖ്യ – Malayalam" lang="ml" hreflang="ml" data-title="ഗോസിയൻ പൂർണ്ണസംഖ്യ" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target"><span>മലയാളം</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Geheel_getal_van_Gauss" title="Geheel getal van Gauss – Dutch" lang="nl" hreflang="nl" data-title="Geheel getal van Gauss" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%82%AC%E3%82%A6%E3%82%B9%E6%95%B4%E6%95%B0" title="ガウス整数 – Japanese" lang="ja" hreflang="ja" data-title="ガウス整数" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Gaussisk_heltall" title="Gaussisk heltall – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Gaussisk heltall" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Liczby_ca%C5%82kowite_Gaussa" title="Liczby całkowite Gaussa – Polish" lang="pl" hreflang="pl" data-title="Liczby całkowite Gaussa" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Inteiro_de_Gauss" title="Inteiro de Gauss – Portuguese" lang="pt" hreflang="pt" data-title="Inteiro de Gauss" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ru badge-Q17437798 badge-goodarticle mw-list-item" title="good article badge"><a href="https://ru.wikipedia.org/wiki/%D0%93%D0%B0%D1%83%D1%81%D1%81%D0%BE%D0%B2%D1%8B_%D1%86%D0%B5%D0%BB%D1%8B%D0%B5_%D1%87%D0%B8%D1%81%D0%BB%D0%B0" title="Гауссовы целые числа – Russian" lang="ru" hreflang="ru" data-title="Гауссовы целые числа" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Gaussovo_pra%C5%A1tevilo" title="Gaussovo praštevilo – Slovenian" lang="sl" hreflang="sl" data-title="Gaussovo praštevilo" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Gaussin_kokonaisluku" title="Gaussin kokonaisluku – Finnish" lang="fi" hreflang="fi" data-title="Gaussin kokonaisluku" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Gaussiskt_heltal" title="Gaussiskt heltal – Swedish" lang="sv" hreflang="sv" data-title="Gaussiskt heltal" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%95%E0%AE%BE%E0%AE%9A%E0%AE%BF%E0%AE%AF_%E0%AE%AE%E0%AF%81%E0%AE%B4%E0%AF%81%E0%AE%B5%E0%AF%86%E0%AE%A3%E0%AF%8D" title="காசிய முழுவெண் – Tamil" lang="ta" hreflang="ta" data-title="காசிய முழுவெண்" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%93%D0%B0%D1%83%D1%81%D1%81%D0%BE%D0%B2%D1%96_%D1%87%D0%B8%D1%81%D0%BB%D0%B0" title="Гауссові числа – Ukrainian" lang="uk" hreflang="uk" data-title="Гауссові числа" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/S%E1%BB%91_nguy%C3%AAn_Gauss" title="Số nguyên Gauss – Vietnamese" lang="vi" hreflang="vi" data-title="Số nguyên Gauss" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a 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print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">Not to be confused with <a href="/wiki/Gaussian_integral" title="Gaussian integral">Gaussian integral</a>.</div> <p>In <a href="/wiki/Number_theory" title="Number theory">number theory</a>, a <b>Gaussian integer</b> is a <a href="/wiki/Complex_number" title="Complex number">complex number</a> whose real and imaginary parts are both <a href="/wiki/Integer" title="Integer">integers</a>. The Gaussian integers, with ordinary <a href="/wiki/Addition" title="Addition">addition</a> and <a href="/wiki/Multiplication" title="Multiplication">multiplication</a> of <a href="/wiki/Complex_number" title="Complex number">complex numbers</a>, form an <a href="/wiki/Integral_domain" title="Integral domain">integral domain</a>, usually written as <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathbf {Z} [i]}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="bold">Z</mi> </mrow> <mo stretchy="false">[</mo> <mi>i</mi> <mo stretchy="false">]</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathbf {Z} [i]}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/d0a617cf5867f951fefb72f3ab7278e0f6f1eedd" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:3.73ex; height:2.843ex;" alt="{\displaystyle \mathbf {Z} [i]}"></span> or <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathbb {Z} [i].}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="double-struck">Z</mi> </mrow> <mo stretchy="false">[</mo> <mi>i</mi> <mo stretchy="false">]</mo> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathbb {Z} [i].}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/03900897cdf515bbbc52879377653a871b9efc06" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.293ex; height:2.843ex;" alt="{\displaystyle \mathbb {Z} [i].}"></span><sup id="cite_ref-Fraleigh_1976_286_1-0" class="reference"><a href="#cite_note-Fraleigh_1976_286-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p><p>Gaussian integers share many properties with integers: they form a <a href="/wiki/Euclidean_domain" title="Euclidean domain">Euclidean domain</a>, and have thus a <a href="/wiki/Euclidean_division" title="Euclidean division">Euclidean division</a> and a <a href="/wiki/Euclidean_algorithm" title="Euclidean algorithm">Euclidean algorithm</a>; this implies <a href="/wiki/Unique_factorization" class="mw-redirect" title="Unique factorization">unique factorization</a> and many related properties. However, Gaussian integers do not have a <a href="/wiki/Total_order" title="Total order">total ordering</a> that respects arithmetic. </p><p>Gaussian integers are <a href="/wiki/Algebraic_integer" title="Algebraic integer">algebraic integers</a> and form the simplest ring of <a href="/wiki/Quadratic_integer" title="Quadratic integer">quadratic integers</a>. </p><p>Gaussian integers are named after the German mathematician <a href="/wiki/Carl_Friedrich_Gauss" title="Carl Friedrich Gauss">Carl Friedrich Gauss</a>. </p> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Gaussian_integer_lattice.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Gaussian_integer_lattice.svg/217px-Gaussian_integer_lattice.svg.png" decoding="async" width="217" height="163" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Gaussian_integer_lattice.svg/326px-Gaussian_integer_lattice.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Gaussian_integer_lattice.svg/434px-Gaussian_integer_lattice.svg.png 2x" data-file-width="389" data-file-height="292" /></a><figcaption>Gaussian integers as <a href="/wiki/Lattice_point" class="mw-redirect" title="Lattice point">lattice points</a> in the <a href="/wiki/Complex_plane" title="Complex plane">complex plane</a></figcaption></figure> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Basic_definitions">Basic definitions</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=1" title="Edit section: Basic definitions"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The Gaussian integers are the set<sup id="cite_ref-Fraleigh_1976_286_1-1" class="reference"><a href="#cite_note-Fraleigh_1976_286-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathbf {Z} [i]=\{a+bi\mid a,b\in \mathbf {Z} \},\qquad {\text{ where }}i^{2}=-1.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="bold">Z</mi> </mrow> <mo stretchy="false">[</mo> <mi>i</mi> <mo stretchy="false">]</mo> <mo>=</mo> <mo fence="false" stretchy="false">{</mo> <mi>a</mi> <mo>+</mo> <mi>b</mi> <mi>i</mi> <mo>∣<!-- ∣ --></mo> <mi>a</mi> <mo>,</mo> <mi>b</mi> <mo>∈<!-- ∈ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="bold">Z</mi> </mrow> <mo fence="false" stretchy="false">}</mo> <mo>,</mo> <mspace width="2em" /> <mrow class="MJX-TeXAtom-ORD"> <mtext> where </mtext> </mrow> <msup> <mi>i</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mo>=</mo> <mo>−<!-- − --></mo> <mn>1.</mn> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathbf {Z} [i]=\{a+bi\mid a,b\in \mathbf {Z} \},\qquad {\text{ where }}i^{2}=-1.}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/e1e23ae09a25e0fde987eb1f99eb41e838ce6537" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:46.057ex; height:3.176ex;" alt="{\displaystyle \mathbf {Z} [i]=\{a+bi\mid a,b\in \mathbf {Z} \},\qquad {\text{ where }}i^{2}=-1.}"></span></dd></dl> <p>In other words, a Gaussian integer is a <a href="/wiki/Complex_number" title="Complex number">complex number</a> such that its <a href="/wiki/Real_part" class="mw-redirect" title="Real part">real</a> and <a href="/wiki/Imaginary_part" class="mw-redirect" title="Imaginary part">imaginary parts</a> are both <a href="/wiki/Integer" title="Integer">integers</a>. Since the Gaussian integers are closed under addition and multiplication, they form a <a href="/wiki/Commutative_ring" title="Commutative ring">commutative ring</a>, which is a <a href="/wiki/Subring" title="Subring">subring</a> of the field of complex numbers. It is thus an <a href="/wiki/Integral_domain" title="Integral domain">integral domain</a>. </p><p>When considered within the <a href="/wiki/Complex_plane" title="Complex plane">complex plane</a>, the Gaussian integers constitute the <span class="texhtml">2</span>-dimensional <a href="/wiki/Integer_lattice" title="Integer lattice">integer lattice</a>. </p><p>The <i>conjugate</i> of a Gaussian integer <span class="texhtml"><i>a</i> + <i>bi</i></span> is the Gaussian integer <span class="texhtml"><i>a</i> – <i>bi</i></span>. </p><p>The <a href="/wiki/Field_norm" title="Field norm"><i>norm</i></a> of a Gaussian integer is its product with its conjugate. </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle N(a+bi)=(a+bi)(a-bi)=a^{2}+b^{2}.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>N</mi> <mo stretchy="false">(</mo> <mi>a</mi> <mo>+</mo> <mi>b</mi> <mi>i</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mo stretchy="false">(</mo> <mi>a</mi> <mo>+</mo> <mi>b</mi> <mi>i</mi> <mo stretchy="false">)</mo> <mo stretchy="false">(</mo> <mi>a</mi> <mo>−<!-- − --></mo> <mi>b</mi> <mi>i</mi> <mo stretchy="false">)</mo> <mo>=</mo> <msup> <mi>a</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mo>+</mo> <msup> <mi>b</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle N(a+bi)=(a+bi)(a-bi)=a^{2}+b^{2}.}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/ad2a727f98a600cdef213b3215a50737f4de952a" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:39.122ex; height:3.176ex;" alt="{\displaystyle N(a+bi)=(a+bi)(a-bi)=a^{2}+b^{2}.}"></span></dd></dl> <p>The norm of a Gaussian integer is thus the square of its <a href="/wiki/Absolute_value" title="Absolute value">absolute value</a> as a complex number. The norm of a Gaussian integer is a nonnegative integer, which is a sum of two <a href="/wiki/Square_number" title="Square number">squares</a>. Thus a norm <a href="/wiki/Sum_of_two_squares_theorem" title="Sum of two squares theorem">cannot be of the form <span class="texhtml">4<i>k</i> + 3</span>, with <span class="texhtml"><i>k</i></span> integer</a>. </p><p>The norm is <a href="/wiki/Completely_multiplicative_function" title="Completely multiplicative function">multiplicative</a>, that is, one has<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle N(zw)=N(z)N(w),}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>N</mi> <mo stretchy="false">(</mo> <mi>z</mi> <mi>w</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mi>N</mi> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> <mi>N</mi> <mo stretchy="false">(</mo> <mi>w</mi> <mo stretchy="false">)</mo> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle N(zw)=N(z)N(w),}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/e0a5bf2b8d198337201ab9bcf9c36d858b187c66" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:20.869ex; height:2.843ex;" alt="{\displaystyle N(zw)=N(z)N(w),}"></span></dd></dl> <p>for every pair of Gaussian integers <span class="texhtml"><i>z</i>, <i>w</i></span>. This can be shown directly, or by using the multiplicative property of the modulus of complex numbers. </p><p>The <a href="/wiki/Unit_(ring_theory)" title="Unit (ring theory)">units</a> of the ring of Gaussian integers (that is the Gaussian integers whose <a href="/wiki/Multiplicative_inverse" title="Multiplicative inverse">multiplicative inverse</a> is also a Gaussian integer) are precisely the Gaussian integers with norm 1, that is, 1, –1, <span class="texhtml"><i>i</i></span> and <span class="texhtml">–<i>i</i></span>.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Euclidean_division">Euclidean division</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=2" title="Edit section: Euclidean division"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Gauss-euklid.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/bb/Gauss-euklid.svg/250px-Gauss-euklid.svg.png" decoding="async" width="250" height="203" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/bb/Gauss-euklid.svg/375px-Gauss-euklid.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/bb/Gauss-euklid.svg/500px-Gauss-euklid.svg.png 2x" data-file-width="531" data-file-height="432" /></a><figcaption>Visualization of maximal distance to some Gaussian integer</figcaption></figure> <p>Gaussian integers have a <a href="/wiki/Euclidean_division" title="Euclidean division">Euclidean division</a> (division with remainder) similar to that of <a href="/wiki/Integer" title="Integer">integers</a> and <a href="/wiki/Polynomial" title="Polynomial">polynomials</a>. This makes the Gaussian integers a <a href="/wiki/Euclidean_domain" title="Euclidean domain">Euclidean domain</a>, and implies that Gaussian integers share with integers and polynomials many important properties such as the existence of a <a href="/wiki/Euclidean_algorithm" title="Euclidean algorithm">Euclidean algorithm</a> for computing <a href="/wiki/Greatest_common_divisor" title="Greatest common divisor">greatest common divisors</a>, <a href="/wiki/B%C3%A9zout%27s_identity" title="Bézout's identity">Bézout's identity</a>, the <a href="/wiki/Principal_ideal_domain" title="Principal ideal domain">principal ideal property</a>, <a href="/wiki/Euclid%27s_lemma" title="Euclid's lemma">Euclid's lemma</a>, the <a href="/wiki/Unique_factorization_theorem" class="mw-redirect" title="Unique factorization theorem">unique factorization theorem</a>, and the <a href="/wiki/Chinese_remainder_theorem" title="Chinese remainder theorem">Chinese remainder theorem</a>, all of which can be proved using only Euclidean division. </p><p>A Euclidean division algorithm takes, in the ring of Gaussian integers, a dividend <span class="texhtml"><i>a</i></span> and divisor <span class="texhtml"><i>b</i> ≠ 0</span>, and produces a quotient <span class="texhtml"><i>q</i></span> and remainder <span class="texhtml"><i>r</i></span> such that </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle a=bq+r\quad {\text{and}}\quad N(r)<N(b).}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>a</mi> <mo>=</mo> <mi>b</mi> <mi>q</mi> <mo>+</mo> <mi>r</mi> <mspace width="1em" /> <mrow class="MJX-TeXAtom-ORD"> <mtext>and</mtext> </mrow> <mspace width="1em" /> <mi>N</mi> <mo stretchy="false">(</mo> <mi>r</mi> <mo stretchy="false">)</mo> <mo><</mo> <mi>N</mi> <mo stretchy="false">(</mo> <mi>b</mi> <mo stretchy="false">)</mo> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle a=bq+r\quad {\text{and}}\quad N(r)<N(b).}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/c5bfa05e12471603b88aec1d50027bd5ab58a761" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:32.214ex; height:2.843ex;" alt="{\displaystyle a=bq+r\quad {\text{and}}\quad N(r)<N(b).}"></span></dd></dl> <p>In fact, one may make the remainder smaller: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle a=bq+r\quad {\text{and}}\quad N(r)\leq {\frac {N(b)}{2}}.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>a</mi> <mo>=</mo> <mi>b</mi> <mi>q</mi> <mo>+</mo> <mi>r</mi> <mspace width="1em" /> <mrow class="MJX-TeXAtom-ORD"> <mtext>and</mtext> </mrow> <mspace width="1em" /> <mi>N</mi> <mo stretchy="false">(</mo> <mi>r</mi> <mo stretchy="false">)</mo> <mo>≤<!-- ≤ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mi>N</mi> <mo stretchy="false">(</mo> <mi>b</mi> <mo stretchy="false">)</mo> </mrow> <mn>2</mn> </mfrac> </mrow> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle a=bq+r\quad {\text{and}}\quad N(r)\leq {\frac {N(b)}{2}}.}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/0d1a807c90c999ca3f9ac06cb27e5502eb450044" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.838ex; width:33.051ex; height:5.676ex;" alt="{\displaystyle a=bq+r\quad {\text{and}}\quad N(r)\leq {\frac {N(b)}{2}}.}"></span></dd></dl> <p><span class="anchor" id="unique_remainder"></span>Even with this better inequality, the quotient and the remainder are not necessarily unique, but one may refine the choice to ensure uniqueness. </p><p>To prove this, one may consider the <a href="/wiki/Complex_number" title="Complex number">complex number</a> quotient <span class="texhtml"><i>x</i> + <i>iy</i> = <style data-mw-deduplicate="TemplateStyles:r1214402035">.mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style><span class="sfrac">⁠<span class="tion"><span class="num"><i>a</i></span><span class="sr-only">/</span><span class="den"><i>b</i></span></span>⁠</span></span>. There are unique integers <span class="texhtml"><i>m</i></span> and <span class="texhtml"><i>n</i></span> such that <span class="texhtml">–<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num">1</span><span class="sr-only">/</span><span class="den">2</span></span>⁠</span> < <i>x</i> – <i>m</i> ≤ <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num">1</span><span class="sr-only">/</span><span class="den">2</span></span>⁠</span></span> and <span class="texhtml">–<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num">1</span><span class="sr-only">/</span><span class="den">2</span></span>⁠</span> < <i>y</i> – <i>n</i> ≤ <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num">1</span><span class="sr-only">/</span><span class="den">2</span></span>⁠</span></span>, and thus <span class="texhtml"><i>N</i>(<i>x</i> – <i>m</i> + <i>i</i>(<i>y</i> – <i>n</i>)) ≤ <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num">1</span><span class="sr-only">/</span><span class="den">2</span></span>⁠</span></span>. Taking <span class="texhtml"><i>q</i> = <i>m</i> + <i>in</i></span>, one has </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle a=bq+r,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>a</mi> <mo>=</mo> <mi>b</mi> <mi>q</mi> <mo>+</mo> <mi>r</mi> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle a=bq+r,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/648db44ee70dc0e4933fc4d0b4930d0bc82e2f3d" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:10.931ex; height:2.509ex;" alt="{\displaystyle a=bq+r,}"></span></dd></dl> <p>with </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle r=b{\bigl (}x-m+i(y-n){\bigr )},}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>r</mi> <mo>=</mo> <mi>b</mi> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-OPEN"> <mo maxsize="1.2em" minsize="1.2em">(</mo> </mrow> </mrow> <mi>x</mi> <mo>−<!-- − --></mo> <mi>m</mi> <mo>+</mo> <mi>i</mi> <mo stretchy="false">(</mo> <mi>y</mi> <mo>−<!-- − --></mo> <mi>n</mi> <mo stretchy="false">)</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-CLOSE"> <mo maxsize="1.2em" minsize="1.2em">)</mo> </mrow> </mrow> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle r=b{\bigl (}x-m+i(y-n){\bigr )},}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/72f4fb6a031e780959385bf119b5876dcd6c9cd8" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:24.975ex; height:3.176ex;" alt="{\displaystyle r=b{\bigl (}x-m+i(y-n){\bigr )},}"></span></dd></dl> <p>and </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle N(r)\leq {\frac {N(b)}{2}}.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>N</mi> <mo stretchy="false">(</mo> <mi>r</mi> <mo stretchy="false">)</mo> <mo>≤<!-- ≤ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mi>N</mi> <mo stretchy="false">(</mo> <mi>b</mi> <mo stretchy="false">)</mo> </mrow> <mn>2</mn> </mfrac> </mrow> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle N(r)\leq {\frac {N(b)}{2}}.}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/56e1230008572723dc77ffcb66b63a9cc6db09cc" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.838ex; width:14.373ex; height:5.676ex;" alt="{\displaystyle N(r)\leq {\frac {N(b)}{2}}.}"></span></dd></dl> <p>The choice of <span class="texhtml"><i>x</i> – <i>m</i></span> and <span class="texhtml"><i>y</i> – <i>n</i></span> in a <a href="/wiki/Semi-open_interval" class="mw-redirect" title="Semi-open interval">semi-open interval</a> is required for uniqueness. This definition of Euclidean division may be interpreted geometrically in the complex plane (see the figure), by remarking that the distance from a complex number <span class="texhtml mvar" style="font-style:italic;">ξ</span> to the closest Gaussian integer is at most <span class="texhtml"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num"><span class="nowrap">√<span style="border-top:1px solid; padding:0 0.1em;">2</span></span></span><span class="sr-only">/</span><span class="den">2</span></span>⁠</span></span>.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Principal_ideals">Principal ideals</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=3" title="Edit section: Principal ideals"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Since the ring <span class="texhtml"><i>G</i></span> of Gaussian integers is a Euclidean domain, <span class="texhtml"><i>G</i></span> is a <a href="/wiki/Principal_ideal_domain" title="Principal ideal domain">principal ideal domain</a>, which means that every <a href="/wiki/Ideal_(ring_theory)" title="Ideal (ring theory)">ideal</a> of <span class="texhtml mvar" style="font-style:italic;">G</span> is <a href="/wiki/Principal_ideal" title="Principal ideal">principal</a>. Explicitly, an <a href="/wiki/Ideal_(ring_theory)" title="Ideal (ring theory)">ideal</a> <span class="texhtml mvar" style="font-style:italic;">I</span> is a subset of a ring <span class="texhtml mvar" style="font-style:italic;">R</span> such that every sum of elements of <span class="texhtml mvar" style="font-style:italic;">I</span> and every product of an element of <span class="texhtml mvar" style="font-style:italic;">I</span> by an element of <span class="texhtml mvar" style="font-style:italic;">R</span> belong to <span class="texhtml mvar" style="font-style:italic;">I</span>. An ideal is <a href="/wiki/Principal_ideal" title="Principal ideal">principal</a> if it consists of all multiples of a single element <span class="texhtml"><i>g</i></span>, that is, it has the form </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \{gx\mid x\in G\}.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mo fence="false" stretchy="false">{</mo> <mi>g</mi> <mi>x</mi> <mo>∣<!-- ∣ --></mo> <mi>x</mi> <mo>∈<!-- ∈ --></mo> <mi>G</mi> <mo fence="false" stretchy="false">}</mo> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \{gx\mid x\in G\}.}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/fe7d25693df349b3106625b0474359a9eb4ab917" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:13.352ex; height:2.843ex;" alt="{\displaystyle \{gx\mid x\in G\}.}"></span></dd></dl> <p>In this case, one says that the ideal is <i>generated</i> by <span class="texhtml"><i>g</i></span> or that <span class="texhtml"><i>g</i></span> is a <i>generator</i> of the ideal. </p><p>Every ideal <span class="texhtml"><i>I</i></span> in the ring of the Gaussian integers is principal, because, if one chooses in <span class="texhtml"><i>I</i></span> a nonzero element <span class="texhtml"><i>g</i></span> of minimal norm, for every element <span class="texhtml"><i>x</i></span> of <span class="texhtml"><i>I</i></span>, the remainder of Euclidean division of <span class="texhtml"><i>x</i></span> by <span class="texhtml"><i>g</i></span> belongs also to <span class="texhtml"><i>I</i></span> and has a norm that is smaller than that of <span class="texhtml"><i>g</i></span>; because of the choice of <span class="texhtml"><i>g</i></span>, this norm is zero, and thus the remainder is also zero. That is, one has <span class="texhtml"><i>x</i> = <i>qg</i></span>, where <span class="texhtml"><i>q</i></span> is the quotient. </p><p>For any <span class="texhtml"><i>g</i></span>, the ideal generated by <span class="texhtml"><i>g</i></span> is also generated by any <i>associate</i> of <span class="texhtml"><i>g</i></span>, that is, <span class="texhtml"><i>g</i>, <i>gi</i>, –<i>g</i>, –<i>gi</i></span>; no other element generates the same ideal. As all the generators of an ideal have the same norm, the <i>norm of an ideal</i> is the norm of any of its generators. </p><p><span class="anchor" id="selected_associates"></span>In some circumstances, it is useful to choose, once for all, a generator for each ideal. There are two classical ways for doing that, both considering first the ideals of odd norm. If the <span class="texhtml"><i>g</i> = <i>a</i> + <i>bi</i></span> has an odd norm <span class="texhtml"><i>a</i><sup>2</sup> + <i>b</i><sup>2</sup></span>, then one of <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span> is odd, and the other is even. Thus <span class="texhtml"><i>g</i></span> has exactly one associate with a real part <span class="texhtml"><i>a</i></span> that is odd and positive. In his original paper, <a href="/wiki/Gauss" class="mw-redirect" title="Gauss">Gauss</a> made another choice, by choosing the unique associate such that the remainder of its division by <span class="texhtml">2 + 2<i>i</i></span> is one. In fact, as <span class="texhtml"><i>N</i>(2 + 2<i>i</i>) = 8</span>, the norm of the remainder is not greater than 4. As this norm is odd, and 3 is not the norm of a Gaussian integer, the norm of the remainder is one, that is, the remainder is a unit. Multiplying <span class="texhtml"><i>g</i></span> by the inverse of this unit, one finds an associate that has one as a remainder, when divided by <span class="texhtml">2 + 2<i>i</i></span>. </p><p>If the norm of <span class="texhtml"><i>g</i></span> is even, then either <span class="texhtml"><i>g</i> = 2<sup><i>k</i></sup><i>h</i></span> or <span class="texhtml"><i>g</i> = 2<sup><i>k</i></sup><i>h</i>(1 + <i>i</i>)</span>, where <span class="texhtml"><i>k</i></span> is a positive integer, and <span class="texhtml"><i>N</i>(<i>h</i>)</span> is odd. Thus, one chooses the associate of <span class="texhtml"><i>g</i></span> for getting a <span class="texhtml"><i>h</i></span> which fits the choice of the associates for elements of odd norm. </p> <div class="mw-heading mw-heading2"><h2 id="Gaussian_primes">Gaussian primes</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=4" title="Edit section: Gaussian primes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>As the Gaussian integers form a <a href="/wiki/Principal_ideal_domain" title="Principal ideal domain">principal ideal domain</a> they form also a <a href="/wiki/Unique_factorization_domain" title="Unique factorization domain">unique factorization domain</a>. This implies that a Gaussian integer is <a href="/wiki/Irreducible_element" title="Irreducible element">irreducible</a> (that is, it is not the product of two <a href="/wiki/Unit_(ring_theory)" title="Unit (ring theory)">non-units</a>) if and only if it is <a href="/wiki/Prime_element" title="Prime element">prime</a> (that is, it generates a <a href="/wiki/Prime_ideal" title="Prime ideal">prime ideal</a>). </p><p>The <a href="/wiki/Prime_element" title="Prime element">prime elements</a> of <span class="texhtml"><b>Z</b>[<i>i</i>]</span> are also known as <b>Gaussian primes</b>. An associate of a Gaussian prime is also a Gaussian prime. The conjugate of a Gaussian prime is also a Gaussian prime (this implies that Gaussian primes are symmetric about the real and imaginary axes). </p><p>A positive integer is a Gaussian prime if and only if it is a <a href="/wiki/Prime_number" title="Prime number">prime number</a> that is <a href="/wiki/Congruence_class" class="mw-redirect" title="Congruence class">congruent to</a> 3 <a href="/wiki/Modulo_operator" class="mw-redirect" title="Modulo operator">modulo</a> 4 (that is, it may be written <span class="texhtml">4<i>n</i> + 3</span>, with <span class="texhtml"><i>n</i></span> a nonnegative integer) (sequence <span class="nowrap external"><a href="//oeis.org/A002145" class="extiw" title="oeis:A002145">A002145</a></span> in the <a href="/wiki/On-Line_Encyclopedia_of_Integer_Sequences" title="On-Line Encyclopedia of Integer Sequences">OEIS</a>). The other prime numbers are not Gaussian primes, but each is the product of two conjugate Gaussian primes. </p><p>A Gaussian integer <span class="texhtml"><i>a</i> + <i>bi</i></span> is a Gaussian prime if and only if either: </p> <ul><li>one of <span class="texhtml"><i>a</i>, <i>b</i></span> is zero and the <a href="/wiki/Absolute_value" title="Absolute value">absolute value</a> of the other is a prime number of the form <span class="texhtml">4<i>n</i> + 3</span> (with <span class="texhtml mvar" style="font-style:italic;">n</span> a nonnegative integer), or</li> <li>both are nonzero and <span class="texhtml"><i>a</i><sup>2</sup> + <i>b</i><sup>2</sup></span> is a prime number (which will <i>not</i> be of the form <span class="texhtml">4<i>n</i> + 3</span>).</li></ul> <p>In other words, a Gaussian integer <span class="texhtml"><i>m</i></span> is a Gaussian prime if and only if either its norm is a prime number, or <span class="texhtml"><i>m</i></span> is the product of a unit (<span class="texhtml">±1, ±<i>i</i></span>) and a prime number of the form <span class="texhtml">4<i>n</i> + 3</span>. </p><p>It follows that there are three cases for the factorization of a prime natural number <span class="texhtml"><i>p</i></span> in the Gaussian integers: </p> <ul><li>If <span class="texhtml"><i>p</i></span> is congruent to 3 modulo 4, then it is a Gaussian prime; in the language of <a href="/wiki/Algebraic_number_theory" title="Algebraic number theory">algebraic number theory</a>, <span class="texhtml"><i>p</i></span> is said to be <a href="/wiki/Inert_prime" class="mw-redirect" title="Inert prime">inert</a> in the Gaussian integers.</li> <li>If <span class="texhtml"><i>p</i></span> is congruent to 1 modulo 4, then it is the product of a Gaussian prime by its conjugate, both of which are non-associated Gaussian primes (neither is the product of the other by a unit); <span class="texhtml"><i>p</i></span> is said to be a <a href="/wiki/Decomposed_prime" class="mw-redirect" title="Decomposed prime">decomposed prime</a> in the Gaussian integers. For example, <span class="texhtml">5 = (2 + <i>i</i>)(2 − <i>i</i>)</span> and <span class="texhtml">13 = (3 + 2<i>i</i>)(3 − 2<i>i</i>)</span>.</li> <li>If <span class="texhtml"><i>p</i> = 2</span>, we have <span class="texhtml">2 = (1 + <i>i</i>)(1 − <i>i</i>) = <i>i</i>(1 − <i>i</i>)<sup>2</sup></span>; that is, 2 is the product of the square of a Gaussian prime by a unit; it is the unique <a href="/wiki/Ramification_(mathematics)#In_algebraic_number_theory" title="Ramification (mathematics)">ramified prime</a> in the Gaussian integers.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Unique_factorization">Unique factorization</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=5" title="Edit section: Unique factorization"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>As for every <a href="/wiki/Unique_factorization_domain" title="Unique factorization domain">unique factorization domain</a>, every Gaussian integer may be factored as a product of a <a href="/wiki/Unit_(ring_theory)" title="Unit (ring theory)">unit</a> and Gaussian primes, and this factorization is unique up to the order of the factors, and the replacement of any prime by any of its associates (together with a corresponding change of the unit factor). </p><p>If one chooses, once for all, a fixed Gaussian prime for each <a href="/wiki/Equivalence_class" title="Equivalence class">equivalence class</a> of associated primes, and if one takes only these selected primes in the factorization, then one obtains a prime factorization which is unique up to the order of the factors. With the <a href="#selected_associates">choices described above</a>, the resulting unique factorization has the form </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle u(1+i)^{e_{0}}{p_{1}}^{e_{1}}\cdots {p_{k}}^{e_{k}},}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>u</mi> <mo stretchy="false">(</mo> <mn>1</mn> <mo>+</mo> <mi>i</mi> <msup> <mo stretchy="false">)</mo> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> </mrow> </msup> <msup> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>1</mn> </mrow> </msub> </mrow> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>1</mn> </mrow> </msub> </mrow> </msup> <mo>⋯<!-- ⋯ --></mo> <msup> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>k</mi> </mrow> </msub> </mrow> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>e</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>k</mi> </mrow> </msub> </mrow> </msup> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle u(1+i)^{e_{0}}{p_{1}}^{e_{1}}\cdots {p_{k}}^{e_{k}},}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4ac54202ebef1a4f49064fbc409600c290910b49" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:22.088ex; height:2.843ex;" alt="{\displaystyle u(1+i)^{e_{0}}{p_{1}}^{e_{1}}\cdots {p_{k}}^{e_{k}},}"></span></dd></dl> <p>where <span class="texhtml"><i>u</i></span> is a unit (that is, <span class="texhtml"><i>u</i> ∈ {1, –1, <i>i</i>, –<i>i</i>}</span>), <span class="texhtml"><i>e</i><sub>0</sub></span> and <span class="texhtml"><i>k</i></span> are nonnegative integers, <span class="texhtml"><i>e</i><sub>1</sub>, …, <i>e<sub>k</sub></i></span> are positive integers, and <span class="texhtml"><i>p</i><sub>1</sub>, …, <i>p<sub>k</sub></i></span> are distinct Gaussian primes such that, depending on the choice of selected associates, </p> <ul><li>either <span class="texhtml"><i>p<sub>k</sub></i> = <i>a<sub>k</sub></i> + <i>ib<sub>k</sub></i></span> with <span class="texhtml"><i>a</i></span> odd and positive, and <span class="texhtml"><i>b</i></span> even,</li> <li>or the remainder of the Euclidean division of <span class="texhtml"><i>p<sub>k</sub></i></span> by <span class="texhtml">2 + 2<i>i</i></span> equals 1 (this is Gauss's original choice<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup>).</li></ul> <p>An advantage of the second choice is that the selected associates behave well under products for Gaussian integers of odd norm. On the other hand, the selected associate for the real Gaussian primes are negative integers. For example, the factorization of 231 in the integers, and with the first choice of associates is <span class="nowrap">3 × 7 × 11</span>, while it is <span class="nowrap">(–1) × (–3) × (–7) × (–11)</span> with the second choice. </p> <div class="mw-heading mw-heading2"><h2 id="Gaussian_rationals">Gaussian rationals</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=6" title="Edit section: Gaussian rationals"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/Field_(mathematics)" title="Field (mathematics)">field</a> of <a href="/wiki/Gaussian_rational" title="Gaussian rational">Gaussian rationals</a> is the <a href="/wiki/Field_of_fractions" title="Field of fractions">field of fractions</a> of the ring of Gaussian integers. It consists of the complex numbers whose real and imaginary part are both <a href="/wiki/Rational_number" title="Rational number">rational</a>. </p><p>The ring of Gaussian integers is the <a href="/wiki/Integral_closure" class="mw-redirect" title="Integral closure">integral closure</a> of the integers in the Gaussian rationals. </p><p>This implies that Gaussian integers are <a href="/wiki/Quadratic_integer" title="Quadratic integer">quadratic integers</a> and that a Gaussian rational is a Gaussian integer, if and only if it is a solution of an equation </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle x^{2}+cx+d=0,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msup> <mi>x</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mo>+</mo> <mi>c</mi> <mi>x</mi> <mo>+</mo> <mi>d</mi> <mo>=</mo> <mn>0</mn> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle x^{2}+cx+d=0,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/6bbf1fe0b4e9a5688bce75380a8bebbc5de237e6" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:16.525ex; height:3.009ex;" alt="{\displaystyle x^{2}+cx+d=0,}"></span></dd></dl> <p>with <span class="texhtml"><i>c</i></span> and <span class="texhtml"><i>d</i></span> integers. In fact <span class="texhtml"><i>a</i> + <i>bi</i></span> is solution of the equation </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle x^{2}-2ax+a^{2}+b^{2},}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msup> <mi>x</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mo>−<!-- − --></mo> <mn>2</mn> <mi>a</mi> <mi>x</mi> <mo>+</mo> <msup> <mi>a</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mo>+</mo> <msup> <mi>b</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle x^{2}-2ax+a^{2}+b^{2},}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4378ba496bcf4f795b94d6ac4cd05f2795e73a84" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:19.61ex; height:3.009ex;" alt="{\displaystyle x^{2}-2ax+a^{2}+b^{2},}"></span></dd></dl> <p>and this equation has integer coefficients if and only if <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span> are both integers. </p> <div class="mw-heading mw-heading2"><h2 id="Greatest_common_divisor"><span class="anchor" id="gcd"></span>Greatest common divisor</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=7" title="Edit section: Greatest common divisor"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>As for any <a href="/wiki/Unique_factorization_domain" title="Unique factorization domain">unique factorization domain</a>, a <i><a href="/wiki/Greatest_common_divisor" title="Greatest common divisor">greatest common divisor</a> (gcd)</i> of two Gaussian integers <span class="texhtml"><i>a</i>, <i>b</i></span> is a Gaussian integer <span class="texhtml"><i>d</i></span> that is a common divisor of <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span>, which has all common divisors of <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span> as divisor. That is (where <span class="texhtml">|</span> denotes the <a href="/wiki/Divisibility" class="mw-redirect" title="Divisibility">divisibility</a> relation), </p> <ul><li><span class="texhtml"><i>d</i> | <i>a</i></span> and <span class="texhtml"><i>d</i> | <i>b</i></span>, and</li> <li><span class="texhtml"><i>c</i> | <i>a</i></span> and <span class="texhtml"><i>c</i> | <i>b</i></span> implies <span class="texhtml"><i>c</i> | <i>d</i></span>.</li></ul> <p>Thus, <i>greatest</i> is meant relatively to the divisibility relation, and not for an ordering of the ring (for integers, both meanings of <i>greatest</i> coincide). </p><p>More technically, a greatest common divisor of <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span> is a <a href="/wiki/Ideal_(ring_theory)#Ideal_generated_by_a_set" title="Ideal (ring theory)">generator</a> of the <a href="/wiki/Ideal_(ring_theory)" title="Ideal (ring theory)">ideal</a> generated by <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span> (this characterization is valid for <a href="/wiki/Principal_ideal_domain" title="Principal ideal domain">principal ideal domains</a>, but not, in general, for unique factorization domains). </p><p>The greatest common divisor of two Gaussian integers is not unique, but is defined up to the multiplication by a <a href="/wiki/Unit_(ring_theory)" title="Unit (ring theory)">unit</a>. That is, given a greatest common divisor <span class="texhtml"><i>d</i></span> of <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span>, the greatest common divisors of <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span> are <span class="texhtml"><i>d</i>, –<i>d</i>, <i>id</i></span>, and <span class="texhtml">–<i>id</i></span>. </p><p>There are several ways for computing a greatest common divisor of two Gaussian integers <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span>. When one knows the prime factorizations of <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span>, </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle a=i^{k}\prod _{m}{p_{m}}^{\nu _{m}},\quad b=i^{n}\prod _{m}{p_{m}}^{\mu _{m}},}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>a</mi> <mo>=</mo> <msup> <mi>i</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>k</mi> </mrow> </msup> <munder> <mo>∏<!-- ∏ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </munder> <msup> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>ν<!-- ν --></mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> </msup> <mo>,</mo> <mspace width="1em" /> <mi>b</mi> <mo>=</mo> <msup> <mi>i</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>n</mi> </mrow> </msup> <munder> <mo>∏<!-- ∏ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </munder> <msup> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>μ<!-- μ --></mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> </msup> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle a=i^{k}\prod _{m}{p_{m}}^{\nu _{m}},\quad b=i^{n}\prod _{m}{p_{m}}^{\mu _{m}},}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/a72b8871b50dc93609ed9b4fe325e04969be6d19" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -3.005ex; width:34.455ex; height:5.509ex;" alt="{\displaystyle a=i^{k}\prod _{m}{p_{m}}^{\nu _{m}},\quad b=i^{n}\prod _{m}{p_{m}}^{\mu _{m}},}"></span></dd></dl> <p>where the primes <span class="texhtml"><i>p<sub>m</sub></i></span> are pairwise non associated, and the exponents <span class="texhtml"><i>μ<sub>m</sub></i></span> non-associated, a greatest common divisor is </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \prod _{m}{p_{m}}^{\lambda _{m}},}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <munder> <mo>∏<!-- ∏ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </munder> <msup> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>λ<!-- λ --></mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> </msup> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \prod _{m}{p_{m}}^{\lambda _{m}},}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/af9e64f8fa6e92ac770d8dd793b68df75524f7d1" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -3.005ex; width:9.374ex; height:5.509ex;" alt="{\displaystyle \prod _{m}{p_{m}}^{\lambda _{m}},}"></span></dd></dl> <p>with </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \lambda _{m}=\min(\nu _{m},\mu _{m}).}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>λ<!-- λ --></mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> <mo>=</mo> <mo movablelimits="true" form="prefix">min</mo> <mo stretchy="false">(</mo> <msub> <mi>ν<!-- ν --></mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> <mo>,</mo> <msub> <mi>μ<!-- μ --></mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> <mo stretchy="false">)</mo> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \lambda _{m}=\min(\nu _{m},\mu _{m}).}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/16009ca47cb4b98902f48636dabc44be36dc62e8" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:19.394ex; height:2.843ex;" alt="{\displaystyle \lambda _{m}=\min(\nu _{m},\mu _{m}).}"></span></dd></dl> <p>Unfortunately, except in simple cases, the prime factorization is difficult to compute, and <a href="/wiki/Euclidean_algorithm" title="Euclidean algorithm">Euclidean algorithm</a> leads to a much easier (and faster) computation. This algorithm consists of replacing of the input <span class="texhtml">(<i>a</i>, <i>b</i>)</span> by <span class="texhtml">(<i>b</i>, <i>r</i>)</span>, where <span class="texhtml"><i>r</i></span> is the remainder of the Euclidean division of <span class="texhtml"><i>a</i></span> by <span class="texhtml"><i>b</i></span>, and repeating this operation until getting a zero remainder, that is a pair <span class="texhtml">(<i>d</i>, 0)</span>. This process terminates, because, at each step, the norm of the second Gaussian integer decreases. The resulting <span class="texhtml"><i>d</i></span> is a greatest common divisor, because (at each step) <span class="texhtml"><i>b</i></span> and <span class="texhtml"><i>r</i> = <i>a</i> – <i>bq</i></span> have the same divisors as <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span>, and thus the same greatest common divisor. </p><p>This method of computation works always, but is not as simple as for integers because Euclidean division is more complicated. Therefore, a third method is often preferred for hand-written computations. It consists in remarking that the norm <span class="texhtml"><i>N</i>(<i>d</i>)</span> of the greatest common divisor of <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span> is a common divisor of <span class="texhtml"><i>N</i>(<i>a</i>)</span>, <span class="texhtml"><i>N</i>(<i>b</i>)</span>, and <span class="texhtml"><i>N</i>(<i>a</i> + <i>b</i>)</span>. When the greatest common divisor <span class="texhtml"><i>D</i></span> of these three integers has few factors, then it is easy to test, for common divisor, all Gaussian integers with a norm dividing <span class="texhtml"><i>D</i></span>. </p><p>For example, if <span class="texhtml"><i>a</i> = 5 + 3<i>i</i></span>, and <span class="texhtml"><i>b</i> = 2 – 8<i>i</i></span>, one has <span class="texhtml"><i>N</i>(<i>a</i>) = 34</span>, <span class="texhtml"><i>N</i>(<i>b</i>) = 68</span>, and <span class="texhtml"><i>N</i>(<i>a</i> + <i>b</i>) = 74</span>. As the greatest common divisor of the three norms is 2, the greatest common divisor of <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span> has 1 or 2 as a norm. As a gaussian integer of norm 2 is necessary associated to <span class="texhtml">1 + <i>i</i></span>, and as <span class="texhtml">1 + <i>i</i></span> divides <span class="texhtml"><i>a</i></span> and <span class="texhtml"><i>b</i></span>, then the greatest common divisor is <span class="texhtml">1 + <i>i</i></span>. </p><p>If <span class="texhtml"><i>b</i></span> is replaced by its conjugate <span class="texhtml"><i>b</i> = 2 + 8<i>i</i></span>, then the greatest common divisor of the three norms is 34, the norm of <span class="texhtml"><i>a</i></span>, thus one may guess that the greatest common divisor is <span class="texhtml"><i>a</i></span>, that is, that <span class="texhtml"><i>a</i> | <i>b</i></span>. In fact, one has <span class="texhtml">2 + 8<i>i</i> = (5 + 3<i>i</i>)(1 + <i>i</i>)</span>. </p> <div class="mw-heading mw-heading2"><h2 id="Congruences_and_residue_classes"><span class="anchor" id="congruences"></span>Congruences and residue classes</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=8" title="Edit section: Congruences and residue classes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Given a Gaussian integer <span class="texhtml"><i>z</i><sub>0</sub></span>, called a <i>modulus</i>, two Gaussian integers <span class="texhtml"><i>z</i><sub>1</sub>,<i>z</i><sub>2</sub></span> are <i>congruent modulo</i> <span class="texhtml"><i>z</i><sub>0</sub></span>, if their difference is a multiple of <span class="texhtml"><i>z</i><sub>0</sub></span>, that is if there exists a Gaussian integer <span class="texhtml"><i>q</i></span> such that <span class="texhtml"><i>z</i><sub>1</sub> − <i>z</i><sub>2</sub> = <i>qz</i><sub>0</sub></span>. In other words, two Gaussian integers are congruent modulo <span class="texhtml"><i>z</i><sub>0</sub></span>, if their difference belongs to the <a href="/wiki/Ideal_(ring_theory)" title="Ideal (ring theory)">ideal</a> generated by <span class="texhtml"><i>z</i><sub>0</sub></span>. This is denoted as <span class="texhtml"><i>z</i><sub>1</sub> ≡ <i>z</i><sub>2</sub> (mod <i>z</i><sub>0</sub>)</span>. </p><p>The congruence modulo <span class="texhtml"><i>z</i><sub>0</sub></span> is an <a href="/wiki/Equivalence_relation" title="Equivalence relation">equivalence relation</a> (also called a <a href="/wiki/Congruence_relation" title="Congruence relation">congruence relation</a>), which defines a <a href="/wiki/Partition_of_a_set" title="Partition of a set">partition</a> of the Gaussian integers into <a href="/wiki/Equivalence_class" title="Equivalence class">equivalence classes</a>, called here <a href="/wiki/Congruence_class" class="mw-redirect" title="Congruence class">congruence classes</a> or <i>residue classes</i>. The set of the residue classes is usually denoted <span class="texhtml"><b>Z</b>[<i>i</i>]/<i>z</i><sub>0</sub><b>Z</b>[<i>i</i>]</span>, or <span class="texhtml"><b>Z</b>[<i>i</i>]/<span class="nowrap">⟨<i>z</i><sub>0</sub>⟩</span></span>, or simply <span class="texhtml"><b>Z</b>[<i>i</i>]/<i>z</i><sub>0</sub></span>. </p><p>The residue class of a Gaussian integer <span class="texhtml"><i>a</i></span> is the set </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\bar {a}}:=\left\{z\in \mathbf {Z} [i]\mid z\equiv a{\pmod {z_{0}}}\right\}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>a</mi> <mo stretchy="false">¯<!-- ¯ --></mo> </mover> </mrow> </mrow> <mo>:=</mo> <mrow> <mo>{</mo> <mrow> <mi>z</mi> <mo>∈<!-- ∈ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="bold">Z</mi> </mrow> <mo stretchy="false">[</mo> <mi>i</mi> <mo stretchy="false">]</mo> <mo>∣<!-- ∣ --></mo> <mi>z</mi> <mo>≡<!-- ≡ --></mo> <mi>a</mi> <mrow class="MJX-TeXAtom-ORD"> <mspace width="1em" /> <mo stretchy="false">(</mo> <mi>mod</mi> <mspace width="0.333em" /> <msub> <mi>z</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> <mo>}</mo> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\bar {a}}:=\left\{z\in \mathbf {Z} [i]\mid z\equiv a{\pmod {z_{0}}}\right\}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/fff8f7224fcd09a0b310e70c5211a2283725c677" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:34.132ex; height:2.843ex;" alt="{\displaystyle {\bar {a}}:=\left\{z\in \mathbf {Z} [i]\mid z\equiv a{\pmod {z_{0}}}\right\}}"></span></dd></dl> <p>of all Gaussian integers that are congruent to <span class="texhtml"><i>a</i></span>. It follows that <span class="texhtml"><span style="text-decoration:overline;"><i>a</i></span> = <span style="text-decoration:overline;"><i>b</i></span></span> <a href="/wiki/If_and_only_if" title="If and only if">if and only if</a> <span class="texhtml"><i>a</i> ≡ <i>b</i> (mod <i>z</i><sub>0</sub>)</span>. </p><p>Addition and multiplication are compatible with congruences. This means that <span class="texhtml"><i>a</i><sub>1</sub> ≡ <i>b</i><sub>1</sub> (mod <i>z</i><sub>0</sub>)</span> and <span class="texhtml"><i>a</i><sub>2</sub> ≡ <i>b</i><sub>2</sub> (mod <i>z</i><sub>0</sub>)</span> imply <span class="texhtml"><i>a</i><sub>1</sub> + <i>a</i><sub>2</sub> ≡ <i>b</i><sub>1</sub> + <i>b</i><sub>2</sub> (mod <i>z</i><sub>0</sub>)</span> and <span class="texhtml"><i>a</i><sub>1</sub><i>a</i><sub>2</sub> ≡ <i>b</i><sub>1</sub><i>b</i><sub>2</sub> (mod <i>z</i><sub>0</sub>)</span>. This defines well-defined <a href="/wiki/Operation_(mathematics)" title="Operation (mathematics)">operations</a> (that is independent of the choice of representatives) on the residue classes: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\bar {a}}+{\bar {b}}:={\overline {a+b}}\quad {\text{and}}\quad {\bar {a}}\cdot {\bar {b}}:={\overline {ab}}.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>a</mi> <mo stretchy="false">¯<!-- ¯ --></mo> </mover> </mrow> </mrow> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>b</mi> <mo stretchy="false">¯<!-- ¯ --></mo> </mover> </mrow> </mrow> <mo>:=</mo> <mrow class="MJX-TeXAtom-ORD"> <mover> <mrow> <mi>a</mi> <mo>+</mo> <mi>b</mi> </mrow> <mo accent="false">¯<!-- ¯ --></mo> </mover> </mrow> <mspace width="1em" /> <mrow class="MJX-TeXAtom-ORD"> <mtext>and</mtext> </mrow> <mspace width="1em" /> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>a</mi> <mo stretchy="false">¯<!-- ¯ --></mo> </mover> </mrow> </mrow> <mo>⋅<!-- ⋅ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-ORD"> <mover> <mi>b</mi> <mo stretchy="false">¯<!-- ¯ --></mo> </mover> </mrow> </mrow> <mo>:=</mo> <mrow class="MJX-TeXAtom-ORD"> <mover> <mrow> <mi>a</mi> <mi>b</mi> </mrow> <mo accent="false">¯<!-- ¯ --></mo> </mover> </mrow> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\bar {a}}+{\bar {b}}:={\overline {a+b}}\quad {\text{and}}\quad {\bar {a}}\cdot {\bar {b}}:={\overline {ab}}.}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/1f74e762bceab7618ba65b513be6184ea2d117ca" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.505ex; width:33.359ex; height:3.176ex;" alt="{\displaystyle {\bar {a}}+{\bar {b}}:={\overline {a+b}}\quad {\text{and}}\quad {\bar {a}}\cdot {\bar {b}}:={\overline {ab}}.}"></span></dd></dl> <p>With these operations, the residue classes form a <a href="/wiki/Commutative_ring" title="Commutative ring">commutative ring</a>, the <a href="/wiki/Quotient_ring" title="Quotient ring">quotient ring</a> of the Gaussian integers by the ideal generated by <span class="texhtml"><i>z</i><sub>0</sub></span>, which is also traditionally called the <i>residue class ring modulo</i> <span class="texhtml"><i>z</i><sub>0</sub></span> (for more details, see <a href="/wiki/Quotient_ring" title="Quotient ring">Quotient ring</a>). </p> <div class="mw-heading mw-heading3"><h3 id="Examples">Examples</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=9" title="Edit section: Examples"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li>There are exactly two residue classes for the modulus <span class="texhtml">1 + <i>i</i></span>, namely <span class="texhtml"><span style="text-decoration:overline;">0</span> = {0, ±2, ±4,…,±1 ± <i>i</i>, ±3 ± <i>i</i>,…}</span> (all multiples of <span class="texhtml">1 + <i>i</i></span>), and <span class="texhtml"><span style="text-decoration:overline;">1</span> = {±1, ±3, ±5,…, ±<i>i</i>, ±2 ± <i>i</i>,…}</span>, which form a checkerboard pattern in the complex plane. These two classes form thus a ring with two elements, which is, in fact, a <a href="/wiki/Field_(mathematics)" title="Field (mathematics)">field</a>, the unique (up to an isomorphism) field with two elements, and may thus be identified with the <a href="/wiki/Modular_arithmetic" title="Modular arithmetic">integers modulo 2</a>. These two classes may be considered as a generalization of the partition of integers into even and odd integers. Thus one may speak of <i>even</i> and <i>odd</i> Gaussian integers (Gauss divided further even Gaussian integers into <i>even</i>, that is divisible by 2, and <i>half-even</i>).</li> <li>For the modulus 2 there are four residue classes, namely <span class="texhtml"><span style="text-decoration:overline;">0</span>, <span style="text-decoration:overline;">1</span>, <span style="text-decoration:overline;"><i>i</i></span>, <span style="text-decoration:overline;">1 + <i>i</i></span></span>. These form a ring with four elements, in which <span class="texhtml"><i>x</i> = –<i>x</i></span> for every <span class="texhtml"><i>x</i></span>. Thus this ring is not <a href="/wiki/Isomorphic" class="mw-redirect" title="Isomorphic">isomorphic</a> with the ring of integers modulo 4, another ring with four elements. One has <span class="texhtml"><span style="text-decoration:overline;">1 + <i>i</i></span><sup>2</sup> = <span style="text-decoration:overline;">0</span></span>, and thus this ring is not the <a href="/wiki/Finite_field" title="Finite field">finite field</a> with four elements, nor the <a href="/wiki/Direct_product" title="Direct product">direct product</a> of two copies of the ring of integers modulo 2.</li> <li>For the modulus <span class="texhtml">2 + 2i = (<i>i</i> − 1)<sup>3</sup></span> there are eight residue classes, namely <span class="texhtml"><span style="text-decoration:overline;">0</span>, <span style="text-decoration:overline;">±1</span>, <span style="text-decoration:overline;">±<i>i</i></span>, <span style="text-decoration:overline;">1 ± <i>i</i></span>, <span style="text-decoration:overline;">2</span></span>, whereof four contain only even Gaussian integers and four contain only odd Gaussian integers.</li></ul> <div class="mw-heading mw-heading3"><h3 id="Describing_residue_classes">Describing residue classes</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=10" title="Edit section: Describing residue classes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Gauss-Restklassen-wiki.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/19/Gauss-Restklassen-wiki.png/250px-Gauss-Restklassen-wiki.png" decoding="async" width="250" height="250" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/19/Gauss-Restklassen-wiki.png/375px-Gauss-Restklassen-wiki.png 1.5x, //upload.wikimedia.org/wikipedia/commons/1/19/Gauss-Restklassen-wiki.png 2x" data-file-width="400" data-file-height="400" /></a><figcaption>All 13 residue classes with their minimal residues (blue dots) in the square <span class="texhtml"><i>Q</i><sub>00</sub></span> (light green background) for the modulus <span class="texhtml"><i>z</i><sub>0</sub> = 3 + 2<i>i</i></span>. One residue class with <span class="texhtml"><i>z</i> = 2 − 4<i>i</i> ≡ −<i>i</i> (mod <i>z</i><sub>0</sub>)</span> is highlighted with yellow/orange dots.</figcaption></figure> <p>Given a modulus <span class="texhtml"><i>z</i><sub>0</sub></span>, all elements of a residue class have the same remainder for the Euclidean division by <span class="texhtml"><i>z</i><sub>0</sub></span>, provided one uses the division with unique quotient and remainder, which is described <a href="#unique_remainder">above</a>. Thus enumerating the residue classes is equivalent with enumerating the possible remainders. This can be done geometrically in the following way. </p><p>In the <a href="/wiki/Complex_plane" title="Complex plane">complex plane</a>, one may consider a <a href="/wiki/Square_grid" class="mw-redirect" title="Square grid">square grid</a>, whose squares are delimited by the two lines </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\begin{aligned}V_{s}&=\left\{\left.z_{0}\left(s-{\tfrac {1}{2}}+ix\right)\right\vert x\in \mathbf {R} \right\}\quad {\text{and}}\\H_{t}&=\left\{\left.z_{0}\left(x+i\left(t-{\tfrac {1}{2}}\right)\right)\right\vert x\in \mathbf {R} \right\},\end{aligned}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtable columnalign="right left right left right left right left right left right left" rowspacing="3pt" columnspacing="0em 2em 0em 2em 0em 2em 0em 2em 0em 2em 0em" displaystyle="true"> <mtr> <mtd> <msub> <mi>V</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>s</mi> </mrow> </msub> </mtd> <mtd> <mi></mi> <mo>=</mo> <mrow> <mo>{</mo> <mrow> <mrow> <mo fence="true" stretchy="true" symmetric="true"></mo> <mrow> <msub> <mi>z</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mrow> <mo>(</mo> <mrow> <mi>s</mi> <mo>−<!-- − --></mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="false" scriptlevel="0"> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mstyle> </mrow> <mo>+</mo> <mi>i</mi> <mi>x</mi> </mrow> <mo>)</mo> </mrow> </mrow> <mo>|</mo> </mrow> <mi>x</mi> <mo>∈<!-- ∈ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="bold">R</mi> </mrow> </mrow> <mo>}</mo> </mrow> <mspace width="1em" /> <mrow class="MJX-TeXAtom-ORD"> <mtext>and</mtext> </mrow> </mtd> </mtr> <mtr> <mtd> <msub> <mi>H</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>t</mi> </mrow> </msub> </mtd> <mtd> <mi></mi> <mo>=</mo> <mrow> <mo>{</mo> <mrow> <mrow> <mo fence="true" stretchy="true" symmetric="true"></mo> <mrow> <msub> <mi>z</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mrow> <mo>(</mo> <mrow> <mi>x</mi> <mo>+</mo> <mi>i</mi> <mrow> <mo>(</mo> <mrow> <mi>t</mi> <mo>−<!-- − --></mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="false" scriptlevel="0"> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mstyle> </mrow> </mrow> <mo>)</mo> </mrow> </mrow> <mo>)</mo> </mrow> </mrow> <mo>|</mo> </mrow> <mi>x</mi> <mo>∈<!-- ∈ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="bold">R</mi> </mrow> </mrow> <mo>}</mo> </mrow> <mo>,</mo> </mtd> </mtr> </mtable> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\begin{aligned}V_{s}&=\left\{\left.z_{0}\left(s-{\tfrac {1}{2}}+ix\right)\right\vert x\in \mathbf {R} \right\}\quad {\text{and}}\\H_{t}&=\left\{\left.z_{0}\left(x+i\left(t-{\tfrac {1}{2}}\right)\right)\right\vert x\in \mathbf {R} \right\},\end{aligned}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/73271fa220f64f2fe131304274db8df211169239" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -3.171ex; width:38.196ex; height:7.509ex;" alt="{\displaystyle {\begin{aligned}V_{s}&=\left\{\left.z_{0}\left(s-{\tfrac {1}{2}}+ix\right)\right\vert x\in \mathbf {R} \right\}\quad {\text{and}}\\H_{t}&=\left\{\left.z_{0}\left(x+i\left(t-{\tfrac {1}{2}}\right)\right)\right\vert x\in \mathbf {R} \right\},\end{aligned}}}"></span></dd></dl> <p>with <span class="texhtml"><i>s</i></span> and <span class="texhtml"><i>t</i></span> integers (blue lines in the figure). These divide the plane in <a href="/wiki/Semi-open_interval" class="mw-redirect" title="Semi-open interval">semi-open</a> squares (where <span class="texhtml"><i>m</i></span> and <span class="texhtml"><i>n</i></span> are integers) </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle Q_{mn}=\left\{(s+it)z_{0}\left\vert s\in \left[m-{\tfrac {1}{2}},m+{\tfrac {1}{2}}\right),t\in \left[n-{\tfrac {1}{2}},n+{\tfrac {1}{2}}\right)\right.\right\}.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>Q</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> <mi>n</mi> </mrow> </msub> <mo>=</mo> <mrow> <mo>{</mo> <mrow> <mo stretchy="false">(</mo> <mi>s</mi> <mo>+</mo> <mi>i</mi> <mi>t</mi> <mo stretchy="false">)</mo> <msub> <mi>z</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mrow> <mo>|</mo> <mrow> <mi>s</mi> <mo>∈<!-- ∈ --></mo> <mrow> <mo>[</mo> <mrow> <mi>m</mi> <mo>−<!-- − --></mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="false" scriptlevel="0"> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mstyle> </mrow> <mo>,</mo> <mi>m</mi> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="false" scriptlevel="0"> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mstyle> </mrow> </mrow> <mo>)</mo> </mrow> <mo>,</mo> <mi>t</mi> <mo>∈<!-- ∈ --></mo> <mrow> <mo>[</mo> <mrow> <mi>n</mi> <mo>−<!-- − --></mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="false" scriptlevel="0"> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mstyle> </mrow> <mo>,</mo> <mi>n</mi> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="false" scriptlevel="0"> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mstyle> </mrow> </mrow> <mo>)</mo> </mrow> </mrow> <mo fence="true" stretchy="true" symmetric="true"></mo> </mrow> </mrow> <mo>}</mo> </mrow> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle Q_{mn}=\left\{(s+it)z_{0}\left\vert s\in \left[m-{\tfrac {1}{2}},m+{\tfrac {1}{2}}\right),t\in \left[n-{\tfrac {1}{2}},n+{\tfrac {1}{2}}\right)\right.\right\}.}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/2ad979f96c1e4cf630c338899864ef9a861362d6" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.171ex; width:61.928ex; height:3.509ex;" alt="{\displaystyle Q_{mn}=\left\{(s+it)z_{0}\left\vert s\in \left[m-{\tfrac {1}{2}},m+{\tfrac {1}{2}}\right),t\in \left[n-{\tfrac {1}{2}},n+{\tfrac {1}{2}}\right)\right.\right\}.}"></span></dd></dl> <p>The semi-open intervals that occur in the definition of <span class="texhtml"><i>Q<sub>mn</sub></i></span> have been chosen in order that every complex number belong to exactly one square; that is, the squares <span class="texhtml"><i>Q<sub>mn</sub></i></span> form a <a href="/wiki/Partition_(set_theory)" class="mw-redirect" title="Partition (set theory)">partition</a> of the complex plane. One has </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle Q_{mn}=(m+in)z_{0}+Q_{00}=\left\{(m+in)z_{0}+z\mid z\in Q_{00}\right\}.}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>Q</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> <mi>n</mi> </mrow> </msub> <mo>=</mo> <mo stretchy="false">(</mo> <mi>m</mi> <mo>+</mo> <mi>i</mi> <mi>n</mi> <mo stretchy="false">)</mo> <msub> <mi>z</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mo>+</mo> <msub> <mi>Q</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>00</mn> </mrow> </msub> <mo>=</mo> <mrow> <mo>{</mo> <mrow> <mo stretchy="false">(</mo> <mi>m</mi> <mo>+</mo> <mi>i</mi> <mi>n</mi> <mo stretchy="false">)</mo> <msub> <mi>z</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mo>+</mo> <mi>z</mi> <mo>∣<!-- ∣ --></mo> <mi>z</mi> <mo>∈<!-- ∈ --></mo> <msub> <mi>Q</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>00</mn> </mrow> </msub> </mrow> <mo>}</mo> </mrow> <mo>.</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle Q_{mn}=(m+in)z_{0}+Q_{00}=\left\{(m+in)z_{0}+z\mid z\in Q_{00}\right\}.}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/c837b7636248d825945918a98e6528c9caeb969b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:56.165ex; height:2.843ex;" alt="{\displaystyle Q_{mn}=(m+in)z_{0}+Q_{00}=\left\{(m+in)z_{0}+z\mid z\in Q_{00}\right\}.}"></span></dd></dl> <p>This implies that every Gaussian integer is congruent modulo <span class="texhtml"><i>z</i><sub>0</sub></span> to a unique Gaussian integer in <span class="texhtml"><i>Q</i><sub>00</sub></span> (the green square in the figure), which its remainder for the division by <span class="texhtml"><i>z</i><sub>0</sub></span>. In other words, every residue class contains exactly one element in <span class="texhtml"><i>Q</i><sub>00</sub></span>. </p><p>The Gaussian integers in <span class="texhtml"><i>Q</i><sub>00</sub></span> (or in its <a href="/wiki/Boundary_(topology)" title="Boundary (topology)">boundary</a>) are sometimes called <i>minimal residues</i> because their norm are not greater than the norm of any other Gaussian integer in the same residue class (Gauss called them <i>absolutely smallest residues</i>). </p><p>From this one can deduce by geometrical considerations, that the number of residue classes modulo a Gaussian integer <span class="texhtml"><i>z</i><sub>0</sub> = <i>a</i> + <i>bi</i></span> equals its norm <span class="texhtml"><i>N</i>(<i>z</i><sub>0</sub>) = <i>a</i><sup>2</sup> + <i>b</i><sup>2</sup></span> (see below for a proof; similarly, for integers, the number of residue classes modulo <span class="texhtml"><i>n</i></span> is its absolute value <span class="texhtml">|<span class="nowrap" style="padding-left:0.1em; padding-right:0.1em;"><i>n</i></span>|</span>). </p> <style data-mw-deduplicate="TemplateStyles:r1174254338">.mw-parser-output .math_proof{border:thin solid #aaa;margin:1em 2em;padding:0.5em 1em 0.4em}@media(max-width:500px){.mw-parser-output .math_proof{margin:1em 0;padding:0.5em 0.5em 0.4em}}</style><div class="math_proof" style=""><strong>Proof</strong> <p>The relation <span class="texhtml"><i>Q<sub>mn</sub></i> = (<i>m</i> + <i>in</i>)<i>z</i><sub>0</sub> + <i>Q</i><sub>00</sub></span> means that all <span class="texhtml"><i>Q<sub>mn</sub></i></span> are obtained from <span class="texhtml"><i>Q</i><sub>00</sub></span> by <a href="/wiki/Translation_(geometry)" title="Translation (geometry)">translating</a> it by a Gaussian integer. This implies that all <span class="texhtml"><i>Q<sub>mn</sub></i></span> have the same area <span class="texhtml"><i>N</i> = <i>N</i>(<i>z</i><sub>0</sub>)</span>, and contain the same number <span class="texhtml"><i>n<sub>g</sub></i></span> of Gaussian integers. </p><p>Generally, the number of grid points (here the Gaussian integers) in an arbitrary square with the area <span class="texhtml"><i>A</i></span> is <span class="texhtml"><i>A</i> + <i>Θ</i>(<span class="nowrap">√<span style="border-top:1px solid; padding:0 0.1em;"><i>A</i></span></span>)</span> (see <a href="/wiki/Big_theta" class="mw-redirect" title="Big theta">Big theta</a> for the notation). If one considers a big square consisting of <span class="texhtml"><i>k</i> × <i>k</i></span> squares <span class="texhtml"><i>Q<sub>mn</sub></i></span>, then it contains <span class="texhtml"><i>k</i><sup>2</sup><i>N</i> + <i>O</i>(<i>k</i><span class="nowrap">√<span style="border-top:1px solid; padding:0 0.1em;"><i>N</i></span></span>)</span> grid points. It follows <span class="texhtml"><i>k</i><sup>2</sup><i>n<sub>g</sub></i> = <i>k</i><sup>2</sup><i>N</i> + <i>Θ</i>(<i>k</i><span class="nowrap">√<span style="border-top:1px solid; padding:0 0.1em;"><i>N</i></span></span>)</span>, and thus <span class="texhtml"><i>n<sub>g</sub></i> = <i>N</i> + <i>Θ</i>(<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1214402035"><span class="sfrac">⁠<span class="tion"><span class="num"><span class="nowrap">√<span style="border-top:1px solid; padding:0 0.1em;"><i>N</i></span></span></span><span class="sr-only">/</span><span class="den"><i>k</i></span></span>⁠</span>)</span>, after a division by <span class="texhtml"><i>k</i><sup>2</sup></span>. Taking the limit when <span class="texhtml"><i>k</i></span> tends to the infinity gives <span class="texhtml"><i>n<sub>g</sub></i> = <i>N</i> = <i>N</i>(<i>z</i><sub>0</sub>)</span>. </p> </div> <div class="mw-heading mw-heading3"><h3 id="Residue_class_fields">Residue class fields</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=11" title="Edit section: Residue class fields"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The residue class ring modulo a Gaussian integer <span class="texhtml"><i>z</i><sub>0</sub></span> is a <a href="/wiki/Field_(mathematics)" title="Field (mathematics)">field</a> if and only if <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle z_{0}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>z</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle z_{0}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9e72d1d86e86355892b39b8eb32b964834e113bf" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:2.135ex; height:2.009ex;" alt="{\displaystyle z_{0}}"></span> is a Gaussian prime. </p><p>If <span class="texhtml"><i>z</i><sub>0</sub></span> is a decomposed prime or the ramified prime <span class="texhtml">1 + <i>i</i></span> (that is, if its norm <span class="texhtml"><i>N</i>(<i>z</i><sub>0</sub>)</span> is a prime number, which is either 2 or a prime congruent to 1 modulo 4), then the residue class field has a prime number of elements (that is, <span class="texhtml"><i>N</i>(<i>z</i><sub>0</sub>)</span>). It is thus <a href="/wiki/Isomorphic" class="mw-redirect" title="Isomorphic">isomorphic</a> to the field of the integers modulo <span class="texhtml"><i>N</i>(<i>z</i><sub>0</sub>)</span>. </p><p>If, on the other hand, <span class="texhtml"><i>z</i><sub>0</sub></span> is an inert prime (that is, <span class="texhtml"><i>N</i>(<i>z</i><sub>0</sub>) = <i>p</i><sup>2</sup></span> is the square of a prime number, which is congruent to 3 modulo 4), then the residue class field has <span class="texhtml"><i>p</i><sup>2</sup></span> elements, and it is an <a href="/wiki/Field_extension" title="Field extension">extension</a> of degree 2 (unique, up to an isomorphism) of the <a href="/wiki/Prime_field" class="mw-redirect" title="Prime field">prime field</a> with <span class="texhtml"><i>p</i></span> elements (the integers modulo <span class="texhtml"><i>p</i></span>). </p> <div class="mw-heading mw-heading2"><h2 id="Primitive_residue_class_group_and_Euler's_totient_function"><span id="Primitive_residue_class_group_and_Euler.27s_totient_function"></span>Primitive residue class group and Euler's totient function</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=12" title="Edit section: Primitive residue class group and Euler's totient function"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Many theorems (and their proofs) for moduli of integers can be directly transferred to moduli of Gaussian integers, if one replaces the absolute value of the modulus by the norm. This holds especially for the <i>primitive residue class group</i> (also called <a href="/wiki/Multiplicative_group_of_integers_modulo_n" title="Multiplicative group of integers modulo n">multiplicative group of integers modulo <span class="texhtml"><i>n</i></span></a>) and <a href="/wiki/Euler%27s_totient_function" title="Euler's totient function">Euler's totient function</a>. The primitive residue class group of a modulus <span class="texhtml"><i>z</i></span> is defined as the subset of its residue classes, which contains all residue classes <span class="texhtml"><span style="text-decoration:overline;"><i>a</i></span></span> that are coprime to <span class="texhtml"><i>z</i></span>, i.e. <span class="texhtml">(<i>a</i>,<i>z</i>) = 1</span>. Obviously, this system builds a <a href="/wiki/Multiplicative_group" title="Multiplicative group">multiplicative group</a>. The number of its elements shall be denoted by <span class="texhtml"><i>ϕ</i>(<i>z</i>)</span> (analogously to Euler's totient function <span class="texhtml"><i>φ</i>(<i>n</i>)</span> for integers <span class="texhtml"><i>n</i></span>). </p><p>For Gaussian primes it immediately follows that <span class="texhtml"><i>ϕ</i>(<i>p</i>) = |<span class="nowrap" style="padding-left:0.1em; padding-right:0.1em;"><i>p</i></span>|<sup>2</sup> − 1</span> and for arbitrary composite Gaussian integers </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle z=i^{k}\prod _{m}{p_{m}}^{\nu _{m}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>z</mi> <mo>=</mo> <msup> <mi>i</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>k</mi> </mrow> </msup> <munder> <mo>∏<!-- ∏ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </munder> <msup> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>ν<!-- ν --></mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> </msup> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle z=i^{k}\prod _{m}{p_{m}}^{\nu _{m}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/038a7c8e3432ef17c86c0de20a6da431bade1b10" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -3.005ex; width:15.046ex; height:5.509ex;" alt="{\displaystyle z=i^{k}\prod _{m}{p_{m}}^{\nu _{m}}}"></span></dd></dl> <p><a href="/wiki/Euler%27s_totient_function" title="Euler's totient function">Euler's product formula</a> can be derived as </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \phi (z)=\prod _{m\,(\nu _{m}>0)}{\bigl |}{p_{m}}^{\nu _{m}}{\bigr |}^{2}\left(1-{\frac {1}{|p_{m}|{}^{2}}}\right)=|z|^{2}\prod _{p_{m}|z}\left(1-{\frac {1}{|p_{m}|{}^{2}}}\right)}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>ϕ<!-- ϕ --></mi> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> <mo>=</mo> <munder> <mo>∏<!-- ∏ --></mo> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> <mspace width="thinmathspace" /> <mo stretchy="false">(</mo> <msub> <mi>ν<!-- ν --></mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> <mo>></mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </munder> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-OPEN"> <mo maxsize="1.2em" minsize="1.2em">|</mo> </mrow> </mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>ν<!-- ν --></mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> </mrow> </msup> <msup> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-CLOSE"> <mo maxsize="1.2em" minsize="1.2em">|</mo> </mrow> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mrow> <mo>(</mo> <mrow> <mn>1</mn> <mo>−<!-- − --></mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mn>1</mn> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">|</mo> </mrow> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">|</mo> </mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mrow> </mfrac> </mrow> </mrow> <mo>)</mo> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">|</mo> </mrow> <mi>z</mi> <msup> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">|</mo> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <munder> <mo>∏<!-- ∏ --></mo> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">|</mo> </mrow> <mi>z</mi> </mrow> </munder> <mrow> <mo>(</mo> <mrow> <mn>1</mn> <mo>−<!-- − --></mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mn>1</mn> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">|</mo> </mrow> <msub> <mi>p</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>m</mi> </mrow> </msub> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">|</mo> </mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mrow> </mfrac> </mrow> </mrow> <mo>)</mo> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \phi (z)=\prod _{m\,(\nu _{m}>0)}{\bigl |}{p_{m}}^{\nu _{m}}{\bigr |}^{2}\left(1-{\frac {1}{|p_{m}|{}^{2}}}\right)=|z|^{2}\prod _{p_{m}|z}\left(1-{\frac {1}{|p_{m}|{}^{2}}}\right)}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/1f7f71a2bd6a3b6aa56ad822ffd4533297a11004" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -3.505ex; width:60.688ex; height:7.176ex;" alt="{\displaystyle \phi (z)=\prod _{m\,(\nu _{m}>0)}{\bigl |}{p_{m}}^{\nu _{m}}{\bigr |}^{2}\left(1-{\frac {1}{|p_{m}|{}^{2}}}\right)=|z|^{2}\prod _{p_{m}|z}\left(1-{\frac {1}{|p_{m}|{}^{2}}}\right)}"></span></dd></dl> <p>where the product is to build over all prime divisors <span class="texhtml"><i>p<sub>m</sub></i></span> of <span class="texhtml"><i>z</i></span> (with <span class="texhtml"><i>ν<sub>m</sub></i> > 0</span>). Also the important <a href="/wiki/Euler%27s_theorem" title="Euler's theorem">theorem of Euler</a> can be directly transferred: </p> <dl><dd>For all <span class="texhtml"><i>a</i></span> with <span class="texhtml">(<i>a</i>,<i>z</i>) = 1</span>, it holds that <span class="texhtml"><i>a</i><sup><i>ϕ</i>(<i>z</i>)</sup> ≡ 1 (mod <i>z</i>)</span>.</dd></dl> <div class="mw-heading mw-heading2"><h2 id="Historical_background">Historical background</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=13" title="Edit section: Historical background"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The ring of Gaussian integers was introduced by <a href="/wiki/Carl_Friedrich_Gauss" title="Carl Friedrich Gauss">Carl Friedrich Gauss</a> in his second monograph on <a href="/wiki/Quartic_reciprocity" title="Quartic reciprocity">quartic reciprocity</a> (1832).<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> The theorem of <a href="/wiki/Quadratic_reciprocity" title="Quadratic reciprocity">quadratic reciprocity</a> (which he had first succeeded in proving in 1796) relates the solvability of the congruence <span class="texhtml"><i>x</i><sup>2</sup> ≡ <i>q</i> (mod <i>p</i>)</span> to that of <span class="texhtml"><i>x</i><sup>2</sup> ≡ <i>p</i> (mod <i>q</i>)</span>. Similarly, cubic reciprocity relates the solvability of <span class="texhtml"><i>x</i><sup>3</sup> ≡ <i>q</i> (mod <i>p</i>)</span> to that of <span class="texhtml"><i>x</i><sup>3</sup> ≡ <i>p</i> (mod <i>q</i>)</span>, and biquadratic (or quartic) reciprocity is a relation between <span class="texhtml"><i>x</i><sup>4</sup> ≡ <i>q</i> (mod <i>p</i>)</span> and <span class="texhtml"><i>x</i><sup>4</sup> ≡ <i>p</i> (mod <i>q</i>)</span>. Gauss discovered that the law of biquadratic reciprocity and its supplements were more easily stated and proved as statements about "whole complex numbers" (i.e. the Gaussian integers) than they are as statements about ordinary whole numbers (i.e. the integers). </p><p>In a footnote he notes that the <a href="/wiki/Eisenstein_integer" title="Eisenstein integer">Eisenstein integers</a> are the natural domain for stating and proving results on <a href="/wiki/Cubic_reciprocity" title="Cubic reciprocity">cubic reciprocity</a> and indicates that similar extensions of the integers are the appropriate domains for studying higher reciprocity laws. </p><p>This paper not only introduced the Gaussian integers and proved they are a unique factorization domain, it also introduced the terms norm, unit, primary, and associate, which are now standard in algebraic number theory. </p> <div class="mw-heading mw-heading2"><h2 id="Unsolved_problems">Unsolved problems</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=14" title="Edit section: Unsolved problems"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Gauss-primes-768x768.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c8/Gauss-primes-768x768.png/170px-Gauss-primes-768x768.png" decoding="async" width="170" height="170" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c8/Gauss-primes-768x768.png/255px-Gauss-primes-768x768.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c8/Gauss-primes-768x768.png/340px-Gauss-primes-768x768.png 2x" data-file-width="768" data-file-height="768" /></a><figcaption>The distribution of the small Gaussian primes in the complex plane</figcaption></figure> <p>Most of the unsolved problems are related to distribution of Gaussian primes in the plane. </p> <ul><li><a href="/wiki/Gauss%27s_circle_problem" class="mw-redirect" title="Gauss's circle problem">Gauss's circle problem</a> does not deal with the Gaussian integers per se, but instead asks for the number of <a href="/wiki/Lattice_point" class="mw-redirect" title="Lattice point">lattice points</a> inside a circle of a given radius centered at the origin. This is equivalent to determining the number of Gaussian integers with norm less than a given value.</li></ul> <p>There are also conjectures and unsolved problems about the Gaussian primes. Two of them are: </p> <ul><li>The real and imaginary axes have the infinite set of Gaussian primes 3, 7, 11, 19, ... and their associates. Are there any other lines that have infinitely many Gaussian primes on them? In particular, are there infinitely many Gaussian primes of the form <span class="texhtml">1 + <i>ki</i></span>?<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup></li> <li>Is it possible to walk to infinity using the Gaussian primes as stepping stones and taking steps of a uniformly bounded length? This is known as the <a href="/wiki/Gaussian_moat" title="Gaussian moat">Gaussian moat</a> problem; it was posed in 1962 by <a href="/wiki/Basil_Gordon" title="Basil Gordon">Basil Gordon</a> and remains unsolved.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup></li></ul> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=15" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Algebraic_integer" title="Algebraic integer">Algebraic integer</a></li> <li><a href="/wiki/Cyclotomic_field" title="Cyclotomic field">Cyclotomic field</a></li> <li><a href="/wiki/Eisenstein_integer" title="Eisenstein integer">Eisenstein integer</a></li> <li><a href="/wiki/Eisenstein_prime" class="mw-redirect" title="Eisenstein prime">Eisenstein prime</a></li> <li><a href="/wiki/Hurwitz_quaternion" title="Hurwitz quaternion">Hurwitz quaternion</a></li> <li><a href="/wiki/Proofs_of_Fermat%27s_theorem_on_sums_of_two_squares" class="mw-redirect" title="Proofs of Fermat's theorem on sums of two squares">Proofs of Fermat's theorem on sums of two squares</a></li> <li><a href="/wiki/Proofs_of_quadratic_reciprocity" title="Proofs of quadratic reciprocity">Proofs of quadratic reciprocity</a></li> <li><a href="/wiki/Quadratic_integer" title="Quadratic integer">Quadratic integer</a></li> <li><a href="/wiki/Splitting_of_prime_ideals_in_Galois_extensions" title="Splitting of prime ideals in Galois extensions">Splitting of prime ideals in Galois extensions</a> describes the structure of prime ideals in the Gaussian integers</li> <li><a href="/wiki/Table_of_Gaussian_integer_factorizations" title="Table of Gaussian integer factorizations">Table of Gaussian integer factorizations</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="Notes">Notes</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=16" title="Edit section: Notes"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-Fraleigh_1976_286-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-Fraleigh_1976_286_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Fraleigh_1976_286_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFFraleigh1976">Fraleigh (1976</a>, p. 286)</span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><a href="#CITEREFFraleigh1976">Fraleigh (1976</a>, p. 289)</span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><a href="#CITEREFFraleigh1976">Fraleigh (1976</a>, p. 288)</span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><a href="#CITEREFFraleigh1976">Fraleigh (1976</a>, p. 287)</span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><a href="#CITEREFGauss1831">Gauss (1831</a>, p. 546)</span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><a href="#CITEREFKleiner1998">Kleiner (1998)</a></span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text">Ribenboim, Ch.III.4.D Ch. 6.II, Ch. 6.IV (Hardy & Littlewood's conjecture E and F)</span> </li> <li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFGethnerWagonWick1998" class="citation journal cs1">Gethner, Ellen; <a href="/wiki/Stan_Wagon" title="Stan Wagon">Wagon, Stan</a>; Wick, Brian (1998). "A stroll through the Gaussian primes". <i><a href="/wiki/The_American_Mathematical_Monthly" title="The American Mathematical Monthly">The American Mathematical Monthly</a></i>. <b>105</b> (4): 327–337. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.2307%2F2589708">10.2307/2589708</a>. <a href="/wiki/JSTOR_(identifier)" class="mw-redirect" title="JSTOR (identifier)">JSTOR</a> <a rel="nofollow" class="external text" href="https://www.jstor.org/stable/2589708">2589708</a>. <a href="/wiki/MR_(identifier)" class="mw-redirect" title="MR (identifier)">MR</a> <a rel="nofollow" class="external text" href="https://mathscinet.ams.org/mathscinet-getitem?mr=1614871">1614871</a>. <a href="/wiki/Zbl_(identifier)" class="mw-redirect" title="Zbl (identifier)">Zbl</a> <a rel="nofollow" class="external text" href="https://zbmath.org/?format=complete&q=an:0946.11002">0946.11002</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+American+Mathematical+Monthly&rft.atitle=A+stroll+through+the+Gaussian+primes&rft.volume=105&rft.issue=4&rft.pages=327-337&rft.date=1998&rft_id=https%3A%2F%2Fzbmath.org%2F%3Fformat%3Dcomplete%26q%3Dan%3A0946.11002%23id-name%3DZbl&rft_id=https%3A%2F%2Fmathscinet.ams.org%2Fmathscinet-getitem%3Fmr%3D1614871%23id-name%3DMR&rft_id=https%3A%2F%2Fwww.jstor.org%2Fstable%2F2589708%23id-name%3DJSTOR&rft_id=info%3Adoi%2F10.2307%2F2589708&rft.aulast=Gethner&rft.aufirst=Ellen&rft.au=Wagon%2C+Stan&rft.au=Wick%2C+Brian&rfr_id=info%3Asid%2Fen.wikipedia.org%3AGaussian+integer" class="Z3988"></span></span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGuy2004" class="citation book cs1"><a href="/wiki/Richard_K._Guy" title="Richard K. Guy">Guy, Richard K.</a> (2004). <i>Unsolved problems in number theory</i> (3rd ed.). <a href="/wiki/Springer-Verlag" class="mw-redirect" title="Springer-Verlag">Springer-Verlag</a>. pp. 55–57. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-387-20860-2" title="Special:BookSources/978-0-387-20860-2"><bdi>978-0-387-20860-2</bdi></a>. <a href="/wiki/Zbl_(identifier)" class="mw-redirect" title="Zbl (identifier)">Zbl</a> <a rel="nofollow" class="external text" href="https://zbmath.org/?format=complete&q=an:1058.11001">1058.11001</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Unsolved+problems+in+number+theory&rft.pages=55-57&rft.edition=3rd&rft.pub=Springer-Verlag&rft.date=2004&rft_id=https%3A%2F%2Fzbmath.org%2F%3Fformat%3Dcomplete%26q%3Dan%3A1058.11001%23id-name%3DZbl&rft.isbn=978-0-387-20860-2&rft.aulast=Guy&rft.aufirst=Richard+K.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AGaussian+integer" class="Z3988"></span></span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=17" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGauss1831" class="citation cs2">Gauss, C. F. (1831), <a rel="nofollow" class="external text" href="https://babel.hathitrust.org/cgi/pt?id=mdp.39015073697180&view=1up&seq=285">"Theoria residuorum biquadraticorum. Commentatio secunda."</a>, <i>Comm. Soc. Reg. Sci. Göttingen</i>, <b>7</b>: 89–148</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Comm.+Soc.+Reg.+Sci.+G%C3%B6ttingen&rft.atitle=Theoria+residuorum+biquadraticorum.+Commentatio+secunda.&rft.volume=7&rft.pages=89-148&rft.date=1831&rft.aulast=Gauss&rft.aufirst=C.+F.&rft_id=https%3A%2F%2Fbabel.hathitrust.org%2Fcgi%2Fpt%3Fid%3Dmdp.39015073697180%26view%3D1up%26seq%3D285&rfr_id=info%3Asid%2Fen.wikipedia.org%3AGaussian+integer" class="Z3988"></span>; reprinted in Werke, Georg Olms Verlag, Hildesheim, 1973, pp. 93–148. A German translation of this paper is available online in ″H. Maser (ed.): <i><a rel="nofollow" class="external text" href="https://archive.org/details/carlfriedrichga00gausgoog">Carl Friedrich Gauss’ Arithmetische Untersuchungen über höhere Arithmetik.</a></i> Springer, Berlin 1889, pp. 534″.</li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFFraleigh1976" class="citation cs2">Fraleigh, John B. (1976), <i>A First Course In Abstract Algebra</i> (2nd ed.), Reading: <a href="/wiki/Addison-Wesley" title="Addison-Wesley">Addison-Wesley</a>, <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-201-01984-1" title="Special:BookSources/0-201-01984-1"><bdi>0-201-01984-1</bdi></a></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=A+First+Course+In+Abstract+Algebra&rft.place=Reading&rft.edition=2nd&rft.pub=Addison-Wesley&rft.date=1976&rft.isbn=0-201-01984-1&rft.aulast=Fraleigh&rft.aufirst=John+B.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AGaussian+integer" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKleiner1998" class="citation journal cs1">Kleiner, Israel (1998). <a rel="nofollow" class="external text" href="https://ems.press/journals/em/articles/664">"From Numbers to Rings: The Early History of Ring Theory"</a>. <i><a href="/wiki/Elem._Math." class="mw-redirect" title="Elem. Math.">Elem. Math.</a></i> <b>53</b> (1): 18–35. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1007%2Fs000170050029">10.1007/s000170050029</a></span>. <a href="/wiki/Zbl_(identifier)" class="mw-redirect" title="Zbl (identifier)">Zbl</a> <a rel="nofollow" class="external text" href="https://zbmath.org/?format=complete&q=an:0908.16001">0908.16001</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Elem.+Math.&rft.atitle=From+Numbers+to+Rings%3A+The+Early+History+of+Ring+Theory&rft.volume=53&rft.issue=1&rft.pages=18-35&rft.date=1998&rft_id=https%3A%2F%2Fzbmath.org%2F%3Fformat%3Dcomplete%26q%3Dan%3A0908.16001%23id-name%3DZbl&rft_id=info%3Adoi%2F10.1007%2Fs000170050029&rft.aulast=Kleiner&rft.aufirst=Israel&rft_id=https%3A%2F%2Fems.press%2Fjournals%2Fem%2Farticles%2F664&rfr_id=info%3Asid%2Fen.wikipedia.org%3AGaussian+integer" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRibenboim1996" class="citation book cs1"><a href="/wiki/Paulo_Ribenboim" title="Paulo Ribenboim">Ribenboim, Paulo</a> (1996). <i>The New Book of Prime Number Records</i> (3rd ed.). New York: Springer. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-387-94457-5" title="Special:BookSources/0-387-94457-5"><bdi>0-387-94457-5</bdi></a>. <a href="/wiki/Zbl_(identifier)" class="mw-redirect" title="Zbl (identifier)">Zbl</a> <a rel="nofollow" class="external text" href="https://zbmath.org/?format=complete&q=an:0856.11001">0856.11001</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+New+Book+of+Prime+Number+Records&rft.place=New+York&rft.edition=3rd&rft.pub=Springer&rft.date=1996&rft_id=https%3A%2F%2Fzbmath.org%2F%3Fformat%3Dcomplete%26q%3Dan%3A0856.11001%23id-name%3DZbl&rft.isbn=0-387-94457-5&rft.aulast=Ribenboim&rft.aufirst=Paulo&rfr_id=info%3Asid%2Fen.wikipedia.org%3AGaussian+integer" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFHenry_G._Baker1993" class="citation journal cs1">Henry G. Baker (1993). "Complex Gaussian Integers for "Gaussian Graphics"<span class="cs1-kern-right"></span>". <i>ACM SIGPLAN Notices</i>. <b>28</b> (11): 22–27. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1145%2F165564.165571">10.1145/165564.165571</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:8083226">8083226</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=ACM+SIGPLAN+Notices&rft.atitle=Complex+Gaussian+Integers+for+%22Gaussian+Graphics%22&rft.volume=28&rft.issue=11&rft.pages=22-27&rft.date=1993&rft_id=info%3Adoi%2F10.1145%2F165564.165571&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A8083226%23id-name%3DS2CID&rft.au=Henry+G.+Baker&rfr_id=info%3Asid%2Fen.wikipedia.org%3AGaussian+integer" class="Z3988"></span></li></ul> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Gaussian_integer&action=edit&section=18" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20120306225505/http://www.imocompendium.com/index.php?options=mbb%7Ctekstkut&page=0&art=extensions_ddj%7Cf&ttn=Dushan%20D%3Bjukic1%7C%20Arithmetic%20in%20Quadratic%20Fields%7CN%2FA&knj=&p=3nbbw45001">IMO Compendium</a> text on quadratic extensions and Gaussian Integers in problem solving</li> <li>Keith Conrad, <a rel="nofollow" class="external text" href="https://kconrad.math.uconn.edu/blurbs/ugradnumthy/Zinotes.pdf">The Gaussian Integers</a>.</li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl 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of unity</a></li> <li><a href="/wiki/Salem_number" title="Salem number">Salem number</a></li> <li><a href="/wiki/Silver_ratio" title="Silver ratio">Silver ratio (<span class="texhtml mvar" style="font-style:italic;">δ</span><sub><span class="texhtml mvar" style="font-style:italic;">S</span></sub>)</a></li> <li><a href="/wiki/Square_root_of_2" title="Square root of 2">Square root of 2</a></li> <li><a href="/wiki/Square_root_of_3" title="Square root of 3">Square root of 3</a></li> <li><a href="/wiki/Square_root_of_5" title="Square root of 5">Square root of 5</a></li> <li><a href="/wiki/Square_root_of_6" title="Square root of 6">Square root of 6</a></li> <li><a href="/wiki/Square_root_of_7" title="Square root of 7">Square root of 7</a></li> <li><a href="/wiki/Supergolden_ratio" title="Supergolden ratio">Supergolden ratio (<span class="texhtml mvar" style="font-style:italic;">ψ</span>)</a></li> <li><a href="/wiki/Supersilver_ratio" title="Supersilver ratio">Supersilver ratio (<span class="texhtml mvar" style="font-style:italic;">ς</span>)</a></li> <li><a href="/wiki/Twelfth_root_of_2" class="mw-redirect" title="Twelfth root of 2">Twelfth root of 2</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div><b><span class="nowrap"><span class="noviewer" typeof="mw:File"><a href="/wiki/File:Nuvola_apps_edu_mathematics_blue-p.svg" class="mw-file-description"><img alt="icon" src="//upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Nuvola_apps_edu_mathematics_blue-p.svg/16px-Nuvola_apps_edu_mathematics_blue-p.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Nuvola_apps_edu_mathematics_blue-p.svg/24px-Nuvola_apps_edu_mathematics_blue-p.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Nuvola_apps_edu_mathematics_blue-p.svg/32px-Nuvola_apps_edu_mathematics_blue-p.svg.png 2x" data-file-width="128" data-file-height="128" /></a></span> </span><a href="/wiki/Portal:Mathematics" title="Portal:Mathematics">Mathematics portal</a></b></div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Prime_number_classes" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Prime_number_classes" title="Template:Prime number classes"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Prime_number_classes" title="Template talk:Prime number classes"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Prime_number_classes" title="Special:EditPage/Template:Prime number classes"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Prime_number_classes" style="font-size:114%;margin:0 4em"><a href="/wiki/Prime_number" title="Prime number">Prime number</a> classes</div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">By formula</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Fermat_number" title="Fermat number">Fermat (<span class="texhtml texhtml-big" style="font-size:110%;">2<sup>2<sup><i>n</i></sup></sup> + 1</span>)</a></li> <li><a href="/wiki/Mersenne_prime" title="Mersenne prime">Mersenne (<span class="texhtml texhtml-big" style="font-size:110%;">2<sup><i>p</i></sup> − 1</span>)</a></li> <li><a href="/wiki/Double_Mersenne_number" title="Double Mersenne number">Double Mersenne (<span class="texhtml texhtml-big" style="font-size:110%;">2<sup>2<sup><i>p</i></sup>−1</sup> − 1</span>)</a></li> <li><a href="/wiki/Wagstaff_prime" title="Wagstaff prime">Wagstaff <span class="texhtml texhtml-big" style="font-size:110%;">(2<sup><i>p</i></sup> + 1)/3</span></a></li> <li><a href="/wiki/Proth_prime" title="Proth prime">Proth (<span class="texhtml texhtml-big" style="font-size:110%;"><i>k</i>·2<sup><i>n</i></sup> + 1</span>)</a></li> <li><a href="/wiki/Factorial_prime" title="Factorial prime">Factorial (<span class="texhtml texhtml-big" style="font-size:110%;"><i>n</i>! ± 1</span>)</a></li> <li><a href="/wiki/Primorial_prime" title="Primorial prime">Primorial (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p<sub>n</sub></i># ± 1</span>)</a></li> <li><a href="/wiki/Euclid_number" title="Euclid number">Euclid (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p<sub>n</sub></i># + 1</span>)</a></li> <li><a href="/wiki/Pythagorean_prime" title="Pythagorean prime">Pythagorean (<span class="texhtml texhtml-big" style="font-size:110%;">4<i>n</i> + 1</span>)</a></li> <li><a href="/wiki/Pierpont_prime" title="Pierpont prime">Pierpont (<span class="texhtml texhtml-big" style="font-size:110%;">2<sup><i>m</i></sup>·3<sup><i>n</i></sup> + 1</span>)</a></li> <li><a href="/wiki/Quartan_prime" title="Quartan prime">Quartan (<span class="texhtml texhtml-big" style="font-size:110%;"><i>x</i><sup>4</sup> + <i>y</i><sup>4</sup></span>)</a></li> <li><a href="/wiki/Solinas_prime" title="Solinas prime">Solinas (<span class="texhtml texhtml-big" style="font-size:110%;">2<sup><i>m</i></sup> ± 2<sup><i>n</i></sup> ± 1</span>)</a></li> <li><a href="/wiki/Cullen_number" title="Cullen number">Cullen (<span class="texhtml texhtml-big" style="font-size:110%;"><i>n</i>·2<sup><i>n</i></sup> + 1</span>)</a></li> <li><a href="/wiki/Woodall_number" title="Woodall number">Woodall (<span class="texhtml texhtml-big" style="font-size:110%;"><i>n</i>·2<sup><i>n</i></sup> − 1</span>)</a></li> <li><a href="/wiki/Cuban_prime" title="Cuban prime">Cuban (<span class="texhtml texhtml-big" style="font-size:110%;"><i>x</i><sup>3</sup> − <i>y</i><sup>3</sup>)/(<i>x</i> − <i>y</i></span>)</a></li> <li><a href="/wiki/Leyland_number" title="Leyland number">Leyland (<span class="texhtml texhtml-big" style="font-size:110%;"><i>x<sup>y</sup></i> + <i>y<sup>x</sup></i></span>)</a></li> <li><a href="/wiki/Thabit_number" title="Thabit number">Thabit (<span class="texhtml texhtml-big" style="font-size:110%;">3·2<sup><i>n</i></sup> − 1</span>)</a></li> <li><a href="/wiki/Williams_number" title="Williams number">Williams (<span class="texhtml texhtml-big" style="font-size:110%;">(<i>b</i>−1)·<i>b</i><sup><i>n</i></sup> − 1</span>)</a></li> <li><a href="/wiki/Mills%27_constant" title="Mills' constant">Mills (<span class="texhtml texhtml-big" style="font-size:110%;"><span style="font-size:1em">⌊</span><i>A</i><sup>3<sup><i>n</i></sup></sup><span style="font-size:1em">⌋</span></span>)</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">By integer sequence</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Fibonacci_prime" title="Fibonacci prime">Fibonacci</a></li> <li><a href="/wiki/Lucas_prime" class="mw-redirect" title="Lucas prime">Lucas</a></li> <li><a href="/wiki/Pell_prime" class="mw-redirect" title="Pell prime">Pell</a></li> <li><a href="/wiki/Newman%E2%80%93Shanks%E2%80%93Williams_prime" title="Newman–Shanks–Williams prime">Newman–Shanks–Williams</a></li> <li><a href="/wiki/Perrin_prime" class="mw-redirect" title="Perrin prime">Perrin</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">By property</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Wieferich_prime" title="Wieferich prime">Wieferich</a> (<a href="/wiki/Wieferich_pair" title="Wieferich pair">pair</a>)</li> <li><a href="/wiki/Wall%E2%80%93Sun%E2%80%93Sun_prime" title="Wall–Sun–Sun prime">Wall–Sun–Sun</a></li> <li><a href="/wiki/Wolstenholme_prime" title="Wolstenholme prime">Wolstenholme</a></li> <li><a href="/wiki/Wilson_prime" title="Wilson prime">Wilson</a></li> <li><a href="/wiki/Lucky_number" title="Lucky number">Lucky</a></li> <li><a href="/wiki/Fortunate_number" title="Fortunate number">Fortunate</a></li> <li><a href="/wiki/Ramanujan_prime" title="Ramanujan prime">Ramanujan</a></li> <li><a href="/wiki/Pillai_prime" title="Pillai prime">Pillai</a></li> <li><a href="/wiki/Regular_prime" title="Regular prime">Regular</a></li> <li><a href="/wiki/Strong_prime" title="Strong prime">Strong</a></li> <li><a href="/wiki/Stern_prime" title="Stern prime">Stern</a></li> <li><a href="/wiki/Supersingular_prime_(algebraic_number_theory)" title="Supersingular prime (algebraic number theory)">Supersingular (elliptic curve)</a></li> <li><a href="/wiki/Supersingular_prime_(moonshine_theory)" title="Supersingular prime (moonshine theory)">Supersingular (moonshine theory)</a></li> <li><a href="/wiki/Good_prime" title="Good prime">Good</a></li> <li><a href="/wiki/Super-prime" title="Super-prime">Super</a></li> <li><a href="/wiki/Higgs_prime" title="Higgs prime">Higgs</a></li> <li><a href="/wiki/Highly_cototient_number" title="Highly cototient number">Highly cototient</a></li> <li><a href="/wiki/Reciprocals_of_primes#Unique_primes" title="Reciprocals of primes">Unique</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Radix" title="Radix">Base</a>-dependent</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Palindromic_prime" title="Palindromic prime">Palindromic</a></li> <li><a href="/wiki/Emirp" title="Emirp">Emirp</a></li> <li><a href="/wiki/Repunit" title="Repunit">Repunit <span class="texhtml texhtml-big" style="font-size:110%;">(10<sup><i>n</i></sup> − 1)/9</span></a></li> <li><a href="/wiki/Permutable_prime" title="Permutable prime">Permutable</a></li> <li><a href="/wiki/Circular_prime" title="Circular prime">Circular</a></li> <li><a href="/wiki/Truncatable_prime" title="Truncatable prime">Truncatable</a></li> <li><a href="/wiki/Minimal_prime_(recreational_mathematics)" title="Minimal prime (recreational mathematics)">Minimal</a></li> <li><a href="/wiki/Delicate_prime" title="Delicate prime">Delicate</a></li> <li><a href="/wiki/Primeval_number" title="Primeval number">Primeval</a></li> <li><a href="/wiki/Full_reptend_prime" title="Full reptend prime">Full reptend</a></li> <li><a href="/wiki/Unique_prime_number" class="mw-redirect" title="Unique prime number">Unique</a></li> <li><a href="/wiki/Happy_number#Happy_primes" title="Happy number">Happy</a></li> <li><a href="/wiki/Self_number" title="Self number">Self</a></li> <li><a href="/wiki/Smarandache%E2%80%93Wellin_prime" class="mw-redirect" title="Smarandache–Wellin prime">Smarandache–Wellin</a></li> <li><a href="/wiki/Strobogrammatic_prime" class="mw-redirect" title="Strobogrammatic prime">Strobogrammatic</a></li> <li><a href="/wiki/Dihedral_prime" title="Dihedral prime">Dihedral</a></li> <li><a href="/wiki/Tetradic_number" title="Tetradic number">Tetradic</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Patterns</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th id="k-tuples" scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Prime_k-tuple" title="Prime k-tuple"><i>k</i>-tuples</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Twin_prime" title="Twin prime">Twin (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p</i>, <i>p</i> + 2</span>)</a></li> <li><a href="/wiki/Prime_triplet" title="Prime triplet">Triplet (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p</i>, <i>p</i> + 2 or <i>p</i> + 4, <i>p</i> + 6</span>)</a></li> <li><a href="/wiki/Prime_quadruplet" title="Prime quadruplet">Quadruplet (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p</i>, <i>p</i> + 2, <i>p</i> + 6, <i>p</i> + 8</span>)</a></li> <li><a href="/wiki/Cousin_prime" title="Cousin prime">Cousin (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p</i>, <i>p</i> + 4</span>)</a></li> <li><a href="/wiki/Sexy_prime" title="Sexy prime">Sexy (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p</i>, <i>p</i> + 6</span>)</a></li> <li><a href="/wiki/Primes_in_arithmetic_progression" title="Primes in arithmetic progression">Arithmetic progression (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p</i> + <i>a·n</i>, <i>n</i> = 0, 1, 2, 3, ...</span>)</a></li> <li><a href="/wiki/Balanced_prime" title="Balanced prime">Balanced (<span class="texhtml texhtml-big" style="font-size:110%;">consecutive <i>p</i> − <i>n</i>, <i>p</i>, <i>p</i> + <i>n</i></span>)</a></li></ul> </div></td></tr></tbody></table><div> <ul><li><a href="/wiki/Bi-twin_chain" title="Bi-twin chain">Bi-twin chain (<span class="texhtml texhtml-big" style="font-size:110%;"><i>n</i> ± 1, 2<i>n</i> ± 1, 4<i>n</i> ± 1, …</span>)</a></li> <li><a href="/wiki/Chen_prime" title="Chen prime">Chen</a></li> <li><a href="/wiki/Safe_and_Sophie_Germain_primes" title="Safe and Sophie Germain primes">Sophie Germain/Safe (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p</i>, 2<i>p</i> + 1</span>)</a></li> <li><a href="/wiki/Cunningham_chain" title="Cunningham chain">Cunningham (<span class="texhtml texhtml-big" style="font-size:110%;"><i>p</i>, 2<i>p</i> ± 1, 4<i>p</i> ± 3, 8<i>p</i> ± 7, ...</span>)</a></li></ul></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">By size</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <li><a href="/wiki/Megaprime" title="Megaprime">Mega (1,000,000+ digits)</a></li> <li><a href="/wiki/Largest_known_prime_number" title="Largest known prime number">Largest known</a> <ul><li><a href="/wiki/List_of_largest_known_primes_and_probable_primes" title="List of largest known primes and probable primes">list</a></li></ul></li> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Complex_number" title="Complex number">Complex numbers</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Eisenstein_prime" class="mw-redirect" title="Eisenstein prime">Eisenstein prime</a></li> <li><a class="mw-selflink-fragment" href="#Gaussian_primes">Gaussian prime</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Composite_number" title="Composite number">Composite numbers</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Pseudoprime" title="Pseudoprime">Pseudoprime</a> <ul><li><a href="/wiki/Catalan_pseudoprime" title="Catalan pseudoprime">Catalan</a></li> <li><a href="/wiki/Elliptic_pseudoprime" title="Elliptic pseudoprime">Elliptic</a></li> <li><a href="/wiki/Euler_pseudoprime" title="Euler pseudoprime">Euler</a></li> <li><a href="/wiki/Euler%E2%80%93Jacobi_pseudoprime" title="Euler–Jacobi pseudoprime">Euler–Jacobi</a></li> <li><a href="/wiki/Fermat_pseudoprime" title="Fermat pseudoprime">Fermat</a></li> <li><a href="/wiki/Frobenius_pseudoprime" title="Frobenius pseudoprime">Frobenius</a></li> <li><a href="/wiki/Lucas_pseudoprime" title="Lucas pseudoprime">Lucas</a></li> <li><a href="/wiki/Perrin_pseudoprime" class="mw-redirect" title="Perrin pseudoprime">Perrin</a></li> <li><a href="/wiki/Somer%E2%80%93Lucas_pseudoprime" title="Somer–Lucas pseudoprime">Somer–Lucas</a></li> <li><a href="/wiki/Strong_pseudoprime" title="Strong pseudoprime">Strong</a></li></ul></li> <li><a href="/wiki/Carmichael_number" title="Carmichael number">Carmichael number</a></li> <li><a href="/wiki/Almost_prime" title="Almost prime">Almost prime</a></li> <li><a href="/wiki/Semiprime" title="Semiprime">Semiprime</a></li> <li><a href="/wiki/Sphenic_number" title="Sphenic number">Sphenic number</a></li> <li><a href="/wiki/Interprime" title="Interprime">Interprime</a></li> <li><a href="/wiki/Pernicious_number" title="Pernicious number">Pernicious</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related topics</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Probable_prime" title="Probable prime">Probable prime</a></li> <li><a href="/wiki/Industrial-grade_prime" title="Industrial-grade prime">Industrial-grade prime</a></li> <li><a href="/wiki/Illegal_prime" class="mw-redirect" title="Illegal prime">Illegal prime</a></li> <li><a href="/wiki/Formula_for_primes" title="Formula for primes">Formula for primes</a></li> <li><a href="/wiki/Prime_gap" title="Prime gap">Prime gap</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">First 60 primes</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/2" title="2">2</a></li> <li><a href="/wiki/3" title="3">3</a></li> <li><a href="/wiki/5" title="5">5</a></li> <li><a href="/wiki/7" title="7">7</a></li> <li><a href="/wiki/11_(number)" title="11 (number)">11</a></li> <li><a href="/wiki/13_(number)" title="13 (number)">13</a></li> <li><a href="/wiki/17_(number)" title="17 (number)">17</a></li> <li><a href="/wiki/19_(number)" title="19 (number)">19</a></li> <li><a href="/wiki/23_(number)" title="23 (number)">23</a></li> <li><a href="/wiki/29_(number)" title="29 (number)">29</a></li> <li><a href="/wiki/31_(number)" title="31 (number)">31</a></li> <li><a href="/wiki/37_(number)" title="37 (number)">37</a></li> <li><a href="/wiki/41_(number)" title="41 (number)">41</a></li> <li><a href="/wiki/43_(number)" title="43 (number)">43</a></li> <li><a href="/wiki/47_(number)" title="47 (number)">47</a></li> <li><a href="/wiki/53_(number)" title="53 (number)">53</a></li> <li><a href="/wiki/59_(number)" title="59 (number)">59</a></li> <li><a href="/wiki/61_(number)" title="61 (number)">61</a></li> <li><a href="/wiki/67_(number)" title="67 (number)">67</a></li> <li><a href="/wiki/71_(number)" title="71 (number)">71</a></li> <li><a href="/wiki/73_(number)" title="73 (number)">73</a></li> <li><a href="/wiki/79_(number)" title="79 (number)">79</a></li> <li><a href="/wiki/83_(number)" title="83 (number)">83</a></li> <li><a href="/wiki/89_(number)" title="89 (number)">89</a></li> <li><a href="/wiki/97_(number)" title="97 (number)">97</a></li> <li><a href="/wiki/101_(number)" title="101 (number)">101</a></li> <li><a href="/wiki/103_(number)" title="103 (number)">103</a></li> <li><a href="/wiki/107_(number)" title="107 (number)">107</a></li> <li><a href="/wiki/109_(number)" title="109 (number)">109</a></li> <li><a href="/wiki/113_(number)" title="113 (number)">113</a></li> <li><a href="/wiki/127_(number)" title="127 (number)">127</a></li> <li><a href="/wiki/131_(number)" title="131 (number)">131</a></li> <li><a href="/wiki/137_(number)" title="137 (number)">137</a></li> <li><a href="/wiki/139_(number)" title="139 (number)">139</a></li> <li><a href="/wiki/149_(number)" title="149 (number)">149</a></li> <li><a href="/wiki/151_(number)" title="151 (number)">151</a></li> <li><a href="/wiki/157_(number)" title="157 (number)">157</a></li> <li><a href="/wiki/163_(number)" title="163 (number)">163</a></li> <li><a href="/wiki/167_(number)" title="167 (number)">167</a></li> <li><a href="/wiki/173_(number)" title="173 (number)">173</a></li> <li><a href="/wiki/179_(number)" title="179 (number)">179</a></li> <li><a href="/wiki/181_(number)" title="181 (number)">181</a></li> <li><a href="/wiki/191_(number)" title="191 (number)">191</a></li> <li><a href="/wiki/193_(number)" title="193 (number)">193</a></li> <li><a href="/wiki/197_(number)" title="197 (number)">197</a></li> <li><a href="/wiki/199_(number)" title="199 (number)">199</a></li> <li><a href="/wiki/211_(number)" title="211 (number)">211</a></li> <li><a href="/wiki/223_(number)" title="223 (number)">223</a></li> <li><a href="/wiki/227_(number)" title="227 (number)">227</a></li> <li><a href="/wiki/229_(number)" title="229 (number)">229</a></li> <li><a href="/wiki/233_(number)" title="233 (number)">233</a></li> <li><a href="/wiki/239_(number)" title="239 (number)">239</a></li> <li><a href="/wiki/241_(number)" title="241 (number)">241</a></li> <li><a href="/wiki/251_(number)" title="251 (number)">251</a></li> <li><a href="/wiki/257_(number)" title="257 (number)">257</a></li> <li><a href="/wiki/263_(number)" title="263 (number)">263</a></li> <li><a href="/wiki/269_(number)" title="269 (number)">269</a></li> <li><a href="/wiki/271_(number)" title="271 (number)">271</a></li> <li><a href="/wiki/277_(number)" title="277 (number)">277</a></li> <li><a href="/wiki/281_(number)" title="281 (number)">281</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow hlist" colspan="2"><div><a href="/wiki/List_of_prime_numbers" title="List 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