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 A137191 #2 Mar 30 2012 18:49:09 %S A137191 0,0,0,0,0,1,1,4,11,39,120,403,1254,4000,12475,39030 %N A137191 Number of n-celled polyiamonds with perimeter < n+2. %C A137191 These are n-cell polyiamonds with the perimeter less than the maximum possible one. %C A137191 If we associate a graph to a polyiamond with vertices representing cells and edges representing two cells with a common edge, then this sequence enumerates polyiamonds whose corresponding graphs have cycles. %F A137191 A000577(n) - A131481(n) %K A137191 hard,more,nonn %O A137191 1,8 %A A137191 _Tanya Khovanova_, Mar 03 2008