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 A263685 #20 Dec 06 2015 09:59:33
%S A263685 1,1,2,9,33,192,1272,10182,90822,908160,9980160,119761980,1556766780,
%T A263685 21794734080,326918753280,5230700053320,88921859605320,
%U A263685 1600593472880640,30411275148656640,608225502973147920,12772735543856347920,281000181964839321600,6463004184741681561600
%N A263685 Number of inequivalent placements of n nonattacking rooks on n X n board up to rotations of the board.
%H A263685 R. W. Robinson, <a href="http://dx.doi.org/10.1007/BFb0097382">Counting arrangements of bishops</a>, Lect. Notes Math. 560 (1976), 198-214.
%F A263685 For n=4m or n=4m+1, a(n) = (n! + (2m)!*2^(2*m) + (2m)!/m!)/4.
%F A263685 For n=4m+2 or n=4m+3, a(n) = (n! + (2m+1)!*2^(2*m+1))/4.
%F A263685 a(n) = 2*A000903(n) - A000900(n) - A000902(floor(n/2)).
%F A263685 For n>1, a(n) = 2*A000903(n) - A000085(n)/2.
%F A263685 a(n) = (P(n)+G(n)+2*R(n))/4, where P,G,R are defined in Robinson (1976). See also Maple code in A000903.
%t A263685 a[n_] := (r=Mod[n, 4]; m=(n-r)/4; q=Quotient[n, 2]; n! + q!*2^q + 2*If[r <= 1, (2m)!/m!, 0])/4; Array[a, 23] (* _Jean-François Alcover_, Dec 06 2015, adapted from PARI *)
%o A263685 (PARI) { a(n) = ( n! + (n\2)! * 2^(n\2) + 2*if(n%4<=1, (2*(n\4))!/(n\4)! ) )/4; }
%Y A263685 Cf. A000085, A000407, A000899, A000900, A000901, A000902, A000903.
%K A263685 nonn,nice
%O A263685 1,3
%A A263685 _Max Alekseyev_, Oct 31 2015