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A057170
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2-enumeration of 2n X 2n half-turn symmetric alternating-sign matrices.
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1
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1, 2, 12, 288, 26880, 10035200, 14836039680, 87734404251648, 2064716402685640704, 194361783607326689722368, 72958995691997968023051829248, 109548594452892660460226753134067712, 656593430123179564638165745256190909087744, 15741504841171021653720624575980053578961033101312
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OFFSET
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0,2
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LINKS
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MAPLE
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A057170 := proc(n) local i, j, t1; t1 := 2^(n^2); for i to n do for j to n do if j-i mod 2 <> 0 then t1 := t1*(2*j - 2*i + 1)/(2*j - 2*i) end if end do end do; t1 end proc;
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MATHEMATICA
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a[n_] := Module[{t1 = 2^(n^2)}, Do[If[OddQ[j-i], t1 = t1*(2*j - 2*i + 1) / (2*j - 2*i)], {j, n}, {i, n}]; t1];
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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