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 A143880 #5 Oct 20 2014 18:33:06 %S A143880 1,2,3,15,36,383,1505,28764,197391,6544311,74718810 %N A143880 Number of ways of placing kings with no more than 2 mutual attacks on an n X n chessboard symmetric under 180 degree rotation. %K A143880 nonn,more,hard %O A143880 0,2 %A A143880 _R. H. Hardin_, Sep 04 2008