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 A117574 #29 Jul 02 2025 16:02:02 %S A117574 1,1,2,6,20,80,384,2240,15424,123456,1110928,11287232,127016304, %T A117574 1565107248,20935873872,301974271248,4669727780624,77046043259824, %U A117574 1350585114106416,25062108668100208,490725684463001488,10109820295907492304 %N A117574 Total number of permutations p of [n] such that |p(i+3) - p(i)| is not equal to 3 for 1 <= i <= n-3. %C A117574 a(n) is also number of ways to place n nonattacking pieces rook + leaper[3,3] on an n X n chessboard. %H A117574 Vaclav Kotesovec, <a href="/A117574/b117574.txt">Table of n, a(n) for n = 0..30</a> %H A117574 Vaclav Kotesovec, <a href="http://www.kotesovec.cz/books/kotesovec_non_attacking_chess_pieces_2013_6ed.pdf">Non-attacking chess pieces</a>, Sixth edition, p. 633, Feb 02 2013. %H A117574 Vaclav Kotesovec, <a href="/A117574/a117574.txt">Mathematica program for this sequence</a> %H A117574 Roberto Tauraso, <a href="http://www.emis.de/journals/INTEGERS/papers/g11/g11.Abstract.html">The Dinner Table Problem: The Rectangular Case</a>, INTEGERS: Electronic Journal of Combinatorial Number Theory, Vol. 6 (2006), #A11. %F A117574 Formula given in Tauraso reference. %F A117574 Asymptotic (R. Tauraso 2006, quadratic term V. Kotesovec 2011): a(n)/n! ~ (1 + 8/n + 30/n^2)/e^2. %Y A117574 Cf. A002464, A110128. %Y A117574 Column k=3 of A333706. %K A117574 nonn,hard %O A117574 0,3 %A A117574 _James Sellers_, Apr 27 2006 %E A117574 Terms a(17)-a(28) from _Vaclav Kotesovec_, Apr 19 2011 %E A117574 Terms a(29)-a(30) from _Vaclav Kotesovec_, Apr 20 2012 %E A117574 a(0)=1 prepended by _Alois P. Heinz_, Feb 05 2023