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 A138556 #2 Jul 14 2012 13:28:24 %S A138556 36161,36583,56897,59093,67733,69073,74177,81901,98533,98837,104021, %T A138556 110629,110879,110933,149759,155861,157933,173087,173293,175463, %U A138556 179999,199081,207719,217573,223919,229321,235171,235243,240479 %N A138556 Numbers in A137365 but not in A137366. %K A138556 nonn %O A138556 1,1 %A A138556 _Robert G. Wilson v_, Apr 13 2008