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 A143877 #5 Oct 20 2014 18:32:05 %S A143877 1,2,1,7,4,55,17,576,129,13243,1554,465675,35443,32233206,1330673, %T A143877 3746034675,92945020 %N A143877 Number of ways of placing kings with no more than 2 mutual attacks on an n X n chessboard symmetric under horizontal and vertical reflection. %K A143877 nonn,more,hard %O A143877 0,2 %A A143877 _R. H. Hardin_, Sep 04 2008