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 A189857 #8 Aug 04 2025 11:30:27 %S A189857 1,2,6,24,120,720,2952,16064,104800,816160,7327728,74031176,621684168, %T A189857 5950876288,64694543120,777746708096 %N A189857 Number of ways to place n nonattacking composite pieces rook + rider[2,6] on an n X n chessboard. %C A189857 a(n) is also number of permutations p of 1,2,...,n satisfying |p(i+2k)-p(i)|<>6k AND |p(j+6k)-p(j)|<>2k for all i>=1, j>=1, k>=1, i+2k<=n, j+6k<=n. %H A189857 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 A189857 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fairy_chess_piece">Fairy chess piece</a> %Y A189857 Cf. A000170, A189854, A189855, A189856, A189853. %K A189857 nonn,hard %O A189857 1,2 %A A189857 _Vaclav Kotesovec_, Apr 29 2011