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 A143878 #5 Oct 20 2014 18:32:24 %S A143878 1,2,5,17,92,581,4989,54250,776877,14503255,356467268,11553201879, %T A143878 495106836021 %N A143878 Number of ways of placing kings with no more than 2 mutual attacks on an n X n chessboard symmetric about main diagonal. %K A143878 nonn,more,hard %O A143878 0,2 %A A143878 _R. H. Hardin_, Sep 04 2008