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 A189284 #27 Nov 08 2022 02:18:05 %S A189284 1,1,2,6,24,120,696,4572,34260,290328,2751480,28686024,328764732, %T A189284 4106158164,55495145304,806797105320,12554890849992,208164423163908, %U A189284 3663256621120548,68188490015132040,1338490745511631080,27630826605742438968 %N A189284 Number of permutations p of 1,2,...,n satisfying p(i+5)-p(i)<>5 for all 1<=i<=n-5. %C A189284 a(n) is also number of ways to place n nonattacking pieces rook + semi-leaper[5,5] on an n X n chessboard. %H A189284 Vaclav Kotesovec, <a href="/A189284/b189284.txt">Table of n, a(n) for n = 0..26</a> (Updated Jan 19 2019) %H A189284 Vaclav Kotesovec, <a href="https://oeis.org/wiki/User:Vaclav_Kotesovec">Non-attacking chess pieces</a>, 6ed, 2013, p. 644. %H A189284 Vaclav Kotesovec, <a href="/A189284/a189284.txt">Mathematica program for this sequence</a> %H A189284 George Spahn and Doron Zeilberger, <a href="https://arxiv.org/abs/2211.02550">Counting Permutations Where The Difference Between Entries Located r Places Apart Can never be s (For any given positive integers r and s)</a>, arXiv:2211.02550 [math.CO], 2022. %F A189284 Asymptotics (V. Kotesovec, Mar 2011): a(n)/n! ~ (1 + 9/n + 20/n^2)/e. %Y A189284 Cf. A000255, A189281, A189282, A189283, A189256. %K A189284 nonn,hard %O A189284 0,3 %A A189284 _Vaclav Kotesovec_, Apr 19 2011 %E A189284 Terms a(25)-a(26) from _Vaclav Kotesovec_, Apr 20 2012