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 A220986 #7 Dec 29 2012 13:18:35 %S A220986 27961,1105207205101,101005020070200501001, %T A220986 10010005002000700200050010001,1000100005000200007000200005000100001, %U A220986 100001000005000020000070000200000500001000001,10000010000005000002000000700000200000050000010000001 %N A220986 The right Aurifeuillian factor of 10^(20n + 10) + 1. %C A220986 The corresponding left Aurifeuillian factor is A220985. %H A220986 Wikipedia, <a href="http://en.wikipedia.org/wiki/Cunningham_project">Cunningham Project</a> %F A220986 a(n) = 10^(8n + 4) + 10^(7n + 4) + 5 * 10^(6n + 3) + 2 * 10^(5n + 3) + 7 * 10^(4n + 2) + 2 * 10^(3n + 2) + 5 * 10^(2n + 1) + 10^(n + 1) + 1 %F A220986 Aurifeuillian factorization: 10^(20n + 10) + 1 = (10^(4n + 2) + 1) * A220985(n) * a(n) %t A220986 a[n_] := 10^(8n + 4) + 10^(7n + 4) + 5 * 10^(6n + 3) + 2 * 10^(5n + 3) + 7 * 10^(4n + 2) + 2 * 10^(3n + 2) + 5 * 10^(2n + 1) + 10^(n + 1) + 1 %Y A220986 Cf. A092440, A085601, A220978, A198410, A220979, A220980, A220981, A220982 %Y A220986 Cf. A220983, A220984, A220985, A220987, A220988, A220989, A220990 %K A220986 nonn,easy %O A220986 0,1 %A A220986 _Stuart Clary_, Dec 27 2012