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 A220985 #7 Dec 29 2012 15:04:16
%S A220985 3541,904806804901,99004980069800499001,9990004998000699800049990001,
%T A220985 999900004999800006999800004999900001,
%U A220985 99999000004999980000069999800000499999000001,9999990000004999998000000699999800000049999990000001
%N A220985 The left Aurifeuillian factor of 10^(20n+10) + 1.
%C A220985 The corresponding right Aurifeuillian factor is A220986.
%H A220985 Wikipedia, <a href="http://en.wikipedia.org/wiki/Cunningham_project">Cunningham Project</a>
%F A220985 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 A220985 Aurifeuillian factorization: 10^(20n+10) + 1 = (10^(4n+2) + 1) * a(n) * A220986(n).
%t A220985 Table[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, {n, 0, 20}]
%Y A220985 Cf. A092440, A085601, A220978, A198410, A220979-A220990.
%K A220985 nonn,easy
%O A220985 0,1
%A A220985 _Stuart Clary_, Dec 27 2012