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 A133398 #3 Mar 30 2012 17:33:50 %S A133398 1,2,4,5,6,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27, %T A133398 28,29,30,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51, %U A133398 52,53,54,55,56,57,58,59,60,61,62,63,64 %N A133398 Numbers that are not Mersenne primes. %C A133398 Numbers that are not in A000668. %C A133398 Terms a(1) to a(2042) coincide with those of A138836, but then a(2043)=2047 <> A138836(2043)=2048. %Y A133398 Cf. A000037, A014092. Mersenne primes: A000668. %Y A133398 Cf. A138836. %K A133398 easy,nonn %O A133398 1,2 %A A133398 _Omar E. Pol_, Nov 22 2007, Apr 05 2008