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A235324
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Sum of all parts of all partitions of n into an even number of parts minus the sum of all parts of all partitions of n into an odd number of parts.
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2
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-1, 0, -3, 4, -5, 6, -7, 16, -18, 20, -22, 36, -39, 42, -60, 80, -85, 90, -114, 140, -168, 176, -207, 264, -300, 312, -378, 448, -493, 540, -620, 736, -825, 884, -1015, 1188, -1295, 1406, -1599, 1840, -2009, 2184, -2451, 2772, -3060, 3312, -3666, 4176, -4557
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OFFSET
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1,3
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COMMENTS
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Zero together with the absolute values of this sequence give A330373. - Omar E. Pol, Dec 31 2019
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LINKS
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FORMULA
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G.f.: x*f'(x), where f(x) = Product_{k > 0} (1 - x^(2*k - 1)).
a(n) ~ (-1)^n * exp(Pi*sqrt(n/6)) * n^(1/4) / (2^(7/4) * 3^(1/4)). - Vaclav Kotesovec, Nov 21 2016
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EXAMPLE
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There are 12 partitions of 8 into an even number of parts and 10 into an odd number of parts, so that a(8) = 12*8 - 10*8 = 16.
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MATHEMATICA
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Table[n*SeriesCoefficient[Product[1-x^k, {k, 1, n, 2}], {x, 0, n}], {n, 70}]
nmax = 60; Rest[CoefficientList[Series[x*D[Product[1/(1 + x^k), {k, 1, nmax}], x], {x, 0, nmax}], x]] (* Vaclav Kotesovec, Nov 21 2016 *)
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PROG
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(PARI) a(n)= my(A); n*if(n<0, 0, A= x*O(x^n); polcoeff(eta(x+A)/eta(x^2+A), n));
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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STATUS
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approved
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