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 A165769 #13 Sep 28 2015 21:41:41 %S A165769 29,11,4679,131063,123817,318949,209510599,49977801259,2199023255531, %T A165769 9334079,7250118529,2305843009213693921,17457916757373919459, %U A165769 27748320404471,717308900550128276543,2028240960365167042394725128581,221537999297485978817301176713390723 %N A165769 Largest prime factor of the semiprime 2^A165767(n)-A165767(n). %C A165769 A165768(n)=2 <=> A165767(n)=2k for some k <=> a(n)=4^k/2-k is prime. This is the case for k=3,9,21,31,1125,... %H A165769 Max Alekseyev, <a href="/A165769/b165769.txt">Table of n, a(n) for n = 1..39</a> %F A165769 a(n)=(2^A165767(n)-A165767(n))/A165768(n). %e A165769 46235097144973199564251065756966919577339221 is in this sequence because it is the largest prime factor of the semiprime 2^199-199. %K A165769 nonn %O A165769 1,1 %A A165769 _M. F. Hasler_, Oct 08 2009