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 A220989 #16 Feb 14 2024 02:25:21
%S A220989 7,1657,247969,35821441,5159655937,743006877697,106993187463169,
%T A220989 15407021359595521,2218611104160546817,319479999339664244737,
%U A220989 46005119908998197280769,6624737266944778960896001,953962166440636632998608897
%N A220989 a(n) = 12^(2n+1) - 6 * 12^n + 1: the left Aurifeuillian factor of 12^(6n+3) + 1.
%C A220989 The corresponding right Aurifeuillian factor is A220990.
%H A220989 Wikipedia, <a href="http://en.wikipedia.org/wiki/Cunningham_project">Cunningham Project</a>
%H A220989 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (157,-1884,1728).
%F A220989 Aurifeuillian factorization: 12^(6n+3) + 1 = (12^(2n+1) + 1) * a(n) * A220990(n).
%F A220989 G.f.: -(1008*x^2+558*x+7) / ((x-1)*(12*x-1)*(144*x-1)). [_Colin Barker_, Jan 03 2013]
%t A220989 Table[12^(2n+1) - 6 * 12^n + 1, {n, 0, 20}]
%Y A220989 Cf. A092440, A085601, A220978, A198410, A220979-A220990.
%K A220989 nonn,easy
%O A220989 0,1
%A A220989 _Stuart Clary_, Dec 27 2012