This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A220980 #16 Feb 14 2024 02:21:56
%S A220980 71,19151,10165751,6152578751,3820806643751,2384948876968751,
%T A220980 1490211490478593751,931334495635986718751,582078099253082277343751,
%U A220980 363798066973743438730468751,227373698726297855377246093751,142108550062403118610382324218751
%N A220980 a(n) = 5^(4n+2) + 5^(3n+2) + 3 * 5^(2n+1) + 5^(n+1) + 1: the right Aurifeuillian factor of 5^(10n+5) - 1.
%C A220980 The corresponding left Aurifeuillian factor is A220979.
%H A220980 Wikipedia, <a href="http://en.wikipedia.org/wiki/Cunningham_project">Cunningham Project</a>
%H A220980 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (781,-101530,2538250,-12203125,9765625).
%F A220980 Aurifeuillian factorization: 5^(10n+5) - 1 = (5^(2n+1) - 1) * A220979(n) * a(n).
%F A220980 G.f.: -(27734375*x^4-22687500*x^3+2417450*x^2-36300*x+71) / ((x-1)*(5*x-1)*(25*x-1)*(125*x-1)*(625*x-1)). [_Colin Barker_, Jan 03 2013]
%t A220980 Table[5^(4n+2) + 5^(3n+2) + 3 * 5^(2n+1) + 5^(n+1) + 1, {n, 0, 20}]
%Y A220980 Cf. A092440, A085601, A220978, A198410, A220979-A220990.
%K A220980 nonn,easy
%O A220980 0,1
%A A220980 _Stuart Clary_, Dec 27 2012