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A022630
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Expansion of Product_{m>=1} (1 + m*q^m)^2.
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2
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1, 2, 5, 14, 28, 64, 133, 266, 513, 1000, 1873, 3420, 6257, 11078, 19585, 34192, 58714, 99870, 168858, 281666, 467082, 768994, 1253038, 2030658, 3269551, 5227868, 8304467, 13133256, 20630535, 32250274, 50181624, 77653530, 119634925, 183532470, 280245365
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: exp(2*Sum_{j>=1} Sum_{k>=1} (-1)^(j+1)*k^j*x^(j*k)/j). - Ilya Gutkovskiy, Feb 08 2018
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MATHEMATICA
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nn=34; CoefficientList [Series[ Product[(1 + m*q^m)^2, {m, nn}], {q, 0, nn}], q] (* Robert G. Wilson v, Feb 08 2018 *)
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PROG
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(PARI) m=50; q='q+O('q^m); Vec(prod(n=1, m, (1+n*q^n)^2)) \\ G. C. Greubel, Feb 16 2018
(Magma) Coefficients(&*[(1+m*x^m)^2:m in [1..40]])[1..40] where x is PolynomialRing(Integers()).1; // G. C. Greubel, Feb 16 2018
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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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