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A059487
Number of 2-enumeration of 4n X 4n quarter-turn symmetric alternating-sign matrices.
1
1, 2, 80, 53760, 590413824, 104981650735104, 300931721514121691136, 13874404129378738693891686400, 10274196157891080769280680484929536000, 122089077024940067215877965611538507917950976000, 23266604385482749027479729551862778584550130343015874560000
OFFSET
0,2
LINKS
G. Kuperberg, Symmetry classes of alternating-sign matrices under one roof, arXiv:math/0008184 [math.CO], 2000-2001; [Th. 3].
MAPLE
A059487 := proc(n) local i, j, t1; t1 := (-1)^(n*(n-1)/2)*2^(2*n^2-n); for i to n do for j to n do t1 := t1*(4*j - 4*i + 1)/(j - i + n); end do end do; t1 end proc;
MATHEMATICA
a[n_] := Module[{t1 = (-1)^(n*(n - 1)/2)*2^(2*n^2 - n)}, Do[t1 = t1*(4*j - 4*i + 1)/(j - i + n), {j, n}, {i, n}]; t1];
Array[a, 11, 0] (* Jean-François Alcover, Nov 28 2017, from Maple *)
CROSSREFS
Sequence in context: A351854 A210277 A008563 * A156932 A291331 A369468
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Feb 04 2001
STATUS
approved