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 A143893 #5 Oct 20 2014 18:39:04 %S A143893 1,2,3,19,62,785,3961,92618,796423,31554358,442143014 %N A143893 Number of ways of placing kings with no more than 4 mutual attacks on an n X n chessboard symmetric under 180 degree rotation. %K A143893 nonn,more,hard %O A143893 0,2 %A A143893 _R. H. Hardin_, Sep 04 2008