CINXE.COM

<!DOCTYPE html><html lang="en-US"><head><title>Just a moment...</title><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=Edge"><meta name="robots" content="noindex,nofollow"><meta name="viewport" content="width=device-width,initial-scale=1"><style>*{box-sizing:border-box;margin:0;padding:0}html{line-height:1.15;-webkit-text-size-adjust:100%;color:#313131;font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,Noto Sans,sans-serif,Apple Color Emoji,Segoe UI Emoji,Segoe UI Symbol,Noto Color Emoji}body{display:flex;flex-direction:column;height:100vh;min-height:100vh}.main-content{margin:8rem auto;max-width:60rem;padding-left:1.5rem}@media (width <= 720px){.main-content{margin-top:4rem}}.h2{font-size:1.5rem;font-weight:500;line-height:2.25rem}@media (width <= 720px){.h2{font-size:1.25rem;line-height:1.5rem}}#challenge-error-text{background-image:url(data:image/svg+xml;base64,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);background-repeat:no-repeat;background-size:contain;padding-left:34px}@media (prefers-color-scheme:dark){body{background-color:#222;color:#d9d9d9}}</style><meta http-equiv="refresh" content="390"></head><body class="no-js"><div class="main-wrapper" role="main"><div class="main-content"><noscript><div class="h2"><span id="challenge-error-text">Enable JavaScript and cookies to continue</span></div></noscript></div></div><script>(function(){window._cf_chl_opt={cvId: '3',cZone: "oeis.org",cType: 'managed',cRay: '92bbe8d94df51658',cH: 'uHVjd.Oz2m9No0rxmDNjFuRwABvVs8cGlLmKMD6AgIA-1743886140-1.2.1.1-U_N8AoPgxuIFIqfks.j7oKGs.GoDk4QMBdfrQ0UMHl0ge8sprCdGtezY5SxoG4J3',cUPMDTk: "\/?language=catalan&__cf_chl_tk=hK0rAMaTDgtulKEv6zfGKEcFuoBCiabZWigeiyVTQX4-1743886140-1.0.1.1-aBg6ajfW3maXX4UCBu7YkbFJ9Hk4KNVoJBF3_HhMsjU",cFPWv: 'g',cITimeS: '1743886140',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/?language=catalan&__cf_chl_f_tk=hK0rAMaTDgtulKEv6zfGKEcFuoBCiabZWigeiyVTQX4-1743886140-1.0.1.1-aBg6ajfW3maXX4UCBu7YkbFJ9Hk4KNVoJBF3_HhMsjU",md: "2aKavwmYMqRDS94KlZ9WCl4hVWR5gE8xCyf_b5ONIWY-1743886140-1.2.1.1-TBF4VMndAxOHBRbJ6uSr0Rqldk.bsTc7iAq0N0kpy0TPkBWZmDCA3MS00suxmbEinnwFQ6TUR_w7ImxLlmeY3QWYW2_xs2WyeRcWNK7RuHeHkf.5FIsXALoI0Chm7A4hLufx603LmzLY89kiEOcDPElBtZuxVLOjxHauEjc.Iw1Btl_09O.ccxUWN.JSPFOD.E8oX_Y6hMAjFCWWawnA8ZlpLQUdwXc.4wmF8OW7G7YFYTlkv5ONL84_oSNL8B9jGRPC_58_ptXbPTliACpfswE8me4etO4TVkaC.iDo5S0c1FsfzNuurWuLdNJHxNZT.mJndznqsd4maQBexfbWCjlxcnhqn0cajEo59c_XtHtB0r53O7wTETc8fQNzkpjQU.6zOPPranNUdX9wxcsmRXqqCAq_B0TolgCjn31yHIJK2gcWPZg5iZ3AjMibzhkC1snxDelBlk4ECs3WGIKv6m2dnbIbWFcyVbZXFovNNTniGX2GIkajlbPWLSgXB6utO4TJFK5m4KTE.BLE5dbO5G4ZakvLfGGGuu4CzFBv6JoySg_iixyZr0L5ZKGQlml1zcZ6qC6XR0woT0S2bcNzdG9Ao4so7wFPsgNgUro2O7fPob8XpWoZwulb5Pxx_wWJ.jDIkfLGlQDp7ke2C28P_Du7H0ZSchaBsjQ4jbi8WzFh2qgGfFgcXm69Gkf8jJ6uh.jSvGAG.Lm9zz3fQOGrJam0fM6P5bjIQnvNK5nGdVGLZ1hpjEEa_zOvYmoS0q1jf75V6VOzIV5ElCA3r0ZzR2IJU_YjAh8fWwbLW2K6EpciTCS0cQZ2u0I32lHxFdWL4fmubE71j7JA9ZjfN5q2F1oveuRRWpYlmeRJafOww_Pn7iBjtzGPxE4mlfmgKg2h4GwVezNj3hCW6GvqcRxHZ2HnXkt8LeJTiVBU2AizrgxBrqKbA8BOgZnNbW7cZq2srfv4rrwur97_DmIQ3._1rqlgW9twjPEi_TvwnnWTYO4.a7PqlIbAnmr2h6nbz9H3FDKVkVYGxn8ciTf05JgnDY3FOCIAl8fyyy8oCjyZg34ZLaVPFnVsr4Ol0GR8FfVFVTkRixZHx0xtT9dgvDmOlA",mdrd: "lg3flqJlW94AuV6d.nzsXLqC2tICMM67mKO1tE8SLao-1743886140-1.2.1.1-qEJvc5w.eL4LhqtshxQJh7CU4gJHq0aaQyHY6mnR9OwXxM4Ilw2YQHDoZFlF8KNOTpkzQtoq9NnZ9CkDqONkRoMdl3FHUCN3B_6bRHpQLBOeS360aVEHzrO1rsBwXpKOcr50zN9cx4p.6h1CWEVr0Tf9vq7291eauRMqbPRLCc.cSKBR3bTctx5H3qqi5J1TAkPX2mrxjsI0UWDETcLVqvmE371IqnHFcfvcpNllt9GSuIP2dygp7nyjln6i0ClWoCNoX52.y3hNF1kotLNk.9rcL04eb8eBHKHQyqS29G124dIp_e9mXA8q7FaSDhoLy1G2ofHHpq4uCDgvqXuS9YLHhMAnyXPVk.yqXW8G7yZmTsAJp67PHNWg5m_pF3.nWw6CpBgzfQq_n5L_4AAJAGCVvK2aXPvQfhFYK0GruBFakAPoUHCHF9KQr0GG09c0AkUMlVA6z4xUd5eLFc6YsKvpF5olJvGhazDfkBovyjkXrKVZAV_glUkigg1wlgRPj6SnvxDk7vPSUR1bjzlTHLGE.KWTd1f6c8Seix88svRTRyimJm2EjxpNdxDAgGfPl.Em2v5tFmM5t9eKBA_hmgvGO92HfG9rllo6ihak9TU.wDnCWphmTNeXD1NhgJK65H5PRNrmV.TeSDouJS5c0GADMknbWt8f91cqpQ00GTonQvr8GEXFBhctEaoI5qRWWvqP9S6dMkW2LUrIEy9ax6owydNR4CAhxM4RlXsPWHl29EaCsz3FNKO2VwykDsurgwOCLyTs0VZQUWSQzoCv1s7z_UR7mluU5r3Z4E1E_B3GhbJuTAjFCH_ua9NIv5Cwg6cJK9tiQ_GTtnOQCQ0jAqorZYziUajMFkcDZmlhfCaTNJU4SimeVDs56uNkqg1m7kHiGeodt9nCeb0uWlIi9miEc6ptmwNbW94VvNuf1g5jLOfqHRXX4rU0mWm4Oqc9CmBlM6m3b.D11sfE8UH4Rd.Qbfa9uAWXxbnZEne70W.dE_NGrfYCT_LnlBquy0HCPunM0aJTGrdsWSwyAy7KTUIk4OwFWHHIqNZHPg73KONLTanb6HqZOskb73TAtLP4sD1NWaENK6K16lXsIUaMJSS9GkB7o2yfPs6lvKGzfycP1hSwejOnIlLAKcH4K5HfUPT0A6.6cciiiU3MYnes6.Jxh2j_EUOXod9h3Ffx2KGueYel5IjTUEYvBpnwEO0Fy.QkyHyGGae_QnruzB6O2pDgnzEIbDTBnl7tdZ0aFCoEMafd4SID5vxuCxApmdxSsTmYXMSM3WATPTDsYrAVwckvAL73Fwv_iBaG7BFITryJAnu2yLDzFcUophItTdPrVQcTwnUIf2f24UALwI1L11Bs9m2tRzvlFhLo0HBbB32ue8oAwmw5ypy9wSNX31h6tjGhKRvySXpq_ovF1jLXDrYiURd5Hmyt3Unv3hxDnXf6EI9FgBwkYSmfxzbbU1OnVeHnAAZxXLT_sKhfskpp3YGi27RcfIDHOto92vHLPE1cC57HZT1PhpKcApsDItvrovP2Hg51MDRNBr.cZyZwgqFQFXL1jgvI9kMUqu2D.g4RW4uxGpWRgVcBsAXLVsigmXTx0t7nFd4ufqOslSrp_0HEaLprP2Hg5IC7hZ5vBVmdAO8Tsh3R4bh1ZyLz8w.kOUpQgXjomeb1ZxQid2PZKcVfkQi6033NT.Y5Ft3cS68cAEzHu8Z_jtSMotce78DIIvOurhIHOYJQWg4QUdSkvbbmTWKagqJZs4zs5DxExgCtwRIzDEKwbVoqSg8J63t5vTE09h3uTSYsKcnsnXa5y3jCuSb67VT3bfRCNvCL296vIKaOnxMYEYRI8Y1TcOdlHQEdCg1o174fjTDc9iTNkSTugvqVC9JEn.fhLTxROwct0k.aJYJwVpA_pxPlmZc8piIzU3sAOvjt0zGuHBMFadmjmy6Wqy3t8.JHfT5rHZwcu9YAR4pe9Pn8wcpyr5g7ZSl7nb2f93ozTPgOa8gLpklHvTU.7.d6ah7zAR.EiaDLq5gjRawhvuj8H_z2du6m"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/g/orchestrate/chl_page/v1?ray=92bbe8d94df51658';window._cf_chl_opt.cOgUHash = location.hash === '' && location.href.indexOf('#') !== -1 ? '#' : location.hash;window._cf_chl_opt.cOgUQuery = location.search === '' && location.href.slice(0, location.href.length - window._cf_chl_opt.cOgUHash.length).indexOf('?') !== -1 ? '?' : location.search;if (window.history && window.history.replaceState) {var ogU = location.pathname + window._cf_chl_opt.cOgUQuery + window._cf_chl_opt.cOgUHash;history.replaceState(null, null, "\/?language=catalan&__cf_chl_rt_tk=hK0rAMaTDgtulKEv6zfGKEcFuoBCiabZWigeiyVTQX4-1743886140-1.0.1.1-aBg6ajfW3maXX4UCBu7YkbFJ9Hk4KNVoJBF3_HhMsjU" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>