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 A189870 #6 Sep 12 2015 11:00:25 %S A189870 1,0,0,2,2,4,28,0,20,52,280,1192,5520,20196,115936,701836,4174032, %T A189870 27261284,193428616,1445733328,11133210948 %N A189870 Number of ways to place n nonattacking composite pieces queen + leaper[3,4] on an n X n chessboard. %C A189870 a(n) is also number of permutations p of 1,2,...,n satisfying |p(i+3)-p(i)|<>4 AND |p(j+4)-p(j)|<>3 AND |p(m+k)-p(m)|<>k for all i>=1, j>=1, m>=1, k>=1, i+3<=n, j+4<=n, m+k<=n %H A189870 V. Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Number of ways of placing non-attacking queens, kings, bishops and knights</a> (in English and Czech) %H A189870 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fairy_chess_piece">Fairy chess piece</a> %Y A189870 Cf. A051223, A189865, A189868, A189568 %K A189870 nonn,hard %O A189870 1,4 %A A189870 _Vaclav Kotesovec_, Apr 29 2011