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 A143890 #5 Oct 20 2014 18:36:19 %S A143890 1,2,3,9,16,61,143,802,2265,17236,59156,631443,2686969,39237301, %T A143890 210001256 %N A143890 Number of ways of placing kings with no more than 4 mutual attacks on an n X n chessboard symmetric about both diagonal and antidiagonal. %K A143890 nonn,more,hard %O A143890 0,2 %A A143890 _R. H. Hardin_, Sep 04 2008