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 A143889 #5 Oct 20 2014 18:35:54 %S A143889 1,2,7,33,202,1671,17279,234724,4081665,92343898,2711730350, %T A143889 103991393887,5218390436191 %N A143889 Number of ways of placing kings with no more than 4 mutual attacks on an n X n chessboard symmetric about main diagonal. %K A143889 nonn,more,hard %O A143889 0,2 %A A143889 _R. H. Hardin_, Sep 04 2008