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 A143881 #7 Oct 21 2014 03:41:24 %S A143881 1,2,15,207,6084,292607,23511001,3132847224,693856861039, %T A143881 259806377729539 %N A143881 Number of ways of placing kings with no more than 3 mutual attacks on an n X n chessboard. %Y A143881 Cf. A143870, A143875, A143886. %Y A143881 Cf. A143882, A143883, A143884, A143885. %K A143881 nonn,more,hard %O A143881 0,2 %A A143881 _R. H. Hardin_, Sep 04 2008