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A089814
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Expansion of Product_{k>=1} (1 - q^(10k-5))^2.
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2
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1, 0, 0, 0, 0, -2, 0, 0, 0, 0, 1, 0, 0, 0, 0, -2, 0, 0, 0, 0, 4, 0, 0, 0, 0, -4, 0, 0, 0, 0, 5, 0, 0, 0, 0, -6, 0, 0, 0, 0, 9, 0, 0, 0, 0, -12, 0, 0, 0, 0, 13, 0, 0, 0, 0, -16, 0, 0, 0, 0, 21, 0, 0, 0, 0, -26, 0, 0, 0, 0, 29, 0, 0, 0, 0, -36, 0, 0, 0, 0, 46, 0, 0, 0, 0, -54, 0, 0, 0, 0, 62, 0, 0, 0, 0, -74, 0
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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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MATHEMATICA
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A022597[n_] := SeriesCoefficient[ Product[1 + q^k, {k, n}]^-2, {q, 0, n}]; a[n_] := If[Mod[n, 5] != 0, 0, A022597[n/5]]; a[0] = 1; Table[a[n], {n, 0, 96}] (* Jean-François Alcover, Nov 12 2012, after Michael Somos *)
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PROG
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(PARI) x='x+O(x^100); Vec(prod(k=1, 20, (1-x^(10*k-5))^2)) \\ G. C. Greubel, Oct 20 2018
(Magma) m:=100; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!( (&*[(1-x^(10*k-5))^2: k in [1..20]]))); // G. C. Greubel, Oct 20 2018
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CROSSREFS
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Cf. A022597 (expansion of Product_{m >= 1} (1 + q^m)^(-2)).
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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