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A113037
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Number of solutions to +- 1 +- 2 +- .. +- n = 3.
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2
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0, 0, 1, 0, 0, 3, 5, 0, 0, 23, 39, 0, 0, 219, 396, 0, 0, 2406, 4435, 0, 0, 28431, 53167, 0, 0, 353500, 667874, 0, 0, 4557831, 8675836, 0, 0, 60382450, 115601178, 0, 0, 816998489, 1571272955, 0, 0, 11242173783, 21701318843, 0, 0, 156841667096
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OFFSET
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0,6
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LINKS
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FORMULA
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a(n) is the coefficient of x^3 in product(x^(-k)+x^k, k=1..n).
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MAPLE
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A113037:= proc(n) local i, j, p, t; t:= NULL; for j to n do p:=1; for i to j do p:=p*(x^(-i)+x^i); od; t:=t, coeff(p, x, 3); od; t; end;
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MATHEMATICA
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nmax = 50; d = {1}; a1 = {};
Do[
i = Ceiling[Length[d]/2] + 3;
AppendTo[a1, If[i > Length[d], 0, d[[i]]]];
d = PadLeft[d, Length[d] + 2 n] + PadRight[d, Length[d] + 2 n];
, {n, nmax}];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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