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 A143873 #5 Oct 20 2014 18:30:44 %S A143873 1,2,3,5,8,21,53,158,503,2181,9658,53517,313683,2389270 %N A143873 Number of ways of placing kings with no more than 1 mutual attack on an n X n chessboard symmetric about both diagonal and antidiagonal. %K A143873 nonn,more,hard %O A143873 0,2 %A A143873 _R. H. Hardin_, Sep 04 2008