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 A189873 #6 Sep 12 2015 11:00:25 %S A189873 1,0,0,0,0,0,0,0,0,4,56,18,116,112,408,916,2400,7228,27368,111478, %T A189873 445644,1674860,7624368,38737270,178933064 %N A189873 Number of ways to place n nonattacking composite pieces queen + rider[1,3] on an n X n chessboard. %C A189873 In fairy chess, the rider [1,3] is called a Camelrider. %C A189873 a(n) is also number of permutations p of 1,2,...,n satisfying |p(i+k)-p(i)|<>3k AND |p(j+3k)-p(j)|<>k AND |p(m+k)-p(m)|<>k for all i>=1, j>=1, m>=1, k>=1, i+k<=n, j+3k<=n, m+k<=n %H A189873 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 A189873 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fairy_chess_piece">Fairy chess piece</a> %Y A189873 Cf. A102388, A189850 %K A189873 nonn,hard %O A189873 1,10 %A A189873 _Vaclav Kotesovec_, Apr 29 2011