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 A189790 #19 Apr 21 2021 14:29:20
%S A189790 1,4,6,64,120,2304,5040,147456,362880,14745600,39916800,2123366400,
%T A189790 6227020800,416179814400,1307674368000,106542032486400,
%U A189790 355687428096000,34519618525593600,121645100408832000,13807847410237440000
%N A189790 Number of ways to place n nonattacking bishops on an n X n toroidal board.
%H A189790 Vincenzo Librandi, <a href="/A189790/b189790.txt">Table of n, a(n) for n = 1..200</a>
%H A189790 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 A189790 a(n) = 2^n*((n/2)!)^2 if n is even and a(n) = n! if n is odd.
%F A189790 a(n) = n*(2*n-3)*a(n-2)-(n-3)*n*(n-2)^2*a(n-4). [_Vaclav Kotesovec_, Sep 26 2012]
%F A189790 E.g.f.: 1/(1-x)+x*arcsin(x)/(1-x^2)^(3/2). [_Vaclav Kotesovec_, Sep 26 2012]
%t A189790 Table[If[EvenQ[n],2^n*((n/2)!)^2,n!],{n,1,20}]
%t A189790 Table[n!*SeriesCoefficient[1/(1-x)+x*ArcSin[x]/(1-x^2)^(3/2), {x,0,n}], {n,1,25}] (* _Vaclav Kotesovec_, Sep 26 2012 *)
%Y A189790 Cf. A002465, A002454.
%K A189790 nonn,nice
%O A189790 1,2
%A A189790 _Vaclav Kotesovec_, Apr 27 2011