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 A220990 #20 Feb 14 2024 02:25:44
%S A220990 19,1801,249697,35842177,5159904769,743009863681,106993223294977,
%T A220990 15407021789577217,2218611109320327169,319479999401581608961,
%U A220990 46005119909741205651457,6624737266953695061344257,953962166440743626203987969
%N A220990 a(n) = 12^(2n+1) + 6 * 12^n + 1: the right Aurifeuillian factor of 12^(6n+3) + 1.
%C A220990 The corresponding left Aurifeuillian factor is A220989.
%H A220990 Wikipedia, <a href="http://en.wikipedia.org/wiki/Cunningham_project">Cunningham Project</a>
%H A220990 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (157,-1884,1728).
%F A220990 Aurifeuillian factorization: 12^(6n+3) + 1 = (12^(2n+1) + 1) * A220989(n) * a(n).
%F A220990 G.f.: -(2736*x^2-1182*x+19) / ((x-1)*(12*x-1)*(144*x-1)). - _Colin Barker_, Jan 03 2013
%t A220990 Table[12^(2n+1) + 6 * 12^n + 1, {n, 0, 10}]
%t A220990 LinearRecurrence[{157,-1884,1728},{19,1801,249697},20] (* _Harvey P. Dale_, Mar 26 2022 *)
%o A220990 (PARI) a(n)=12^(2*n+1)+6*12^n+1 \\ _Charles R Greathouse IV_, Sep 28 2015
%Y A220990 Cf. A092440, A085601, A220978, A198410, A220979-A220989.
%K A220990 nonn,easy
%O A220990 0,1
%A A220990 _Stuart Clary_, Dec 27 2012