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 A189570 #9 Mar 19 2017 16:26:06 %S A189570 1,1,2,6,24,120,552,2826,17080,117816,943250,8330356,82954582, %T A189570 915854808,11147075946,147948526182 %N A189570 Number of permutations p of 1,2,...,n satisfying |p(i+4)-p(i)|<>5 and |p(j+5)-p(j)|<>4 for all i=1..n-4, j=1..n-5. %C A189570 a(n) is also the number of ways to place n nonattacking pieces rook + leaper[4,5] on an n X n chessboard. %H A189570 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) %F A189570 Asymptotic: a(n)/n! ~ 1/e^4. %Y A189570 Cf. A137774, A189358, A189563, A189564, A189565, A189566, A189567, A189568, A189569. %K A189570 nonn,more,hard %O A189570 0,3 %A A189570 _Vaclav Kotesovec_, Apr 23 2011