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 A189566 #13 Jul 28 2024 16:57:33 %S A189566 1,2,6,24,60,208,1184,7840,51636,410272,3836456,39971896,455888312, %T A189566 5717233896,78164908748,1153568477544,18263732340736,308795344195456, %U A189566 5550690255143992,105653899427070440,2122307518838927952 %N A189566 Number of permutations p of 1,2,...,n satisfying |p(i+2)-p(i)|<>4 and |p(j+4)-p(j)|<>2 for all i=1..n-2, j=1..n-4. %C A189566 a(n) is also the number of ways to place n nonattacking pieces rook + leaper[2,4] on an n X n chessboard. %H A189566 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 A189566 Asymptotic: a(n)/n! ~ 1/e^4. %Y A189566 Cf. A137774, A189358, A189563, A189564, A189565. %K A189566 nonn,hard,more %O A189566 1,2 %A A189566 _Vaclav Kotesovec_, Apr 23 2011 %E A189566 a(17)-a(21) from _Max Alekseyev_, Jul 28 2024