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 A143884 #5 Oct 20 2014 18:34:20 %S A143884 1,2,3,7,16,41,121,434,1581,7325,35854,219307,1397579,11370922 %N A143884 Number of ways of placing kings with no more than 3 mutual attacks on an n X n chessboard symmetric about both diagonal and antidiagonal. %K A143884 nonn,more,hard %O A143884 0,2 %A A143884 _R. H. Hardin_, Sep 04 2008