A220985 - OEIS

%I #7 Dec 29 2012 15:04:16

%S 3541,904806804901,99004980069800499001,9990004998000699800049990001,

%T 999900004999800006999800004999900001,

%U 99999000004999980000069999800000499999000001,9999990000004999998000000699999800000049999990000001

%N The left Aurifeuillian factor of 10^(20n+10) + 1.

%C The corresponding right Aurifeuillian factor is A220986.

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Cunningham_project">Cunningham Project</a>

%F 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 Aurifeuillian factorization: 10^(20n+10) + 1 = (10^(4n+2) + 1) * a(n) * A220986(n).

%t 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 Cf. A092440, A085601, A220978, A198410, A220979-A220990.

%K nonn,easy

%O 0,1

%A _Stuart Clary_, Dec 27 2012