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 A143871 #5 Oct 20 2014 18:28:44 %S A143871 1,2,3,13,18,425,371,27872,25147,8144945,4679546,6097351181, %T A143871 3118820527,16876586891126,6022295415137 %N A143871 Number of ways of placing kings with no more than 1 mutual attack on an n X n chessboard symmetric under horizontal reflection. %K A143871 nonn,more,hard %O A143871 0,2 %A A143871 _R. H. Hardin_, Sep 04 2008