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A363630
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Expansion of Sum_{k>0} (1/(1+x^k)^3 - 1).
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4
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-3, 3, -13, 18, -24, 21, -39, 63, -68, 48, -81, 127, -108, 87, -170, 216, -174, 156, -213, 294, -302, 201, -303, 497, -375, 276, -474, 537, -468, 426, -531, 777, -686, 462, -726, 965, -744, 573, -938, 1200, -906, 798, -993, 1251, -1306, 831, -1179, 1875, -1314, 1023, -1562, 1722, -1488, 1290, -1698
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OFFSET
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1,1
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LINKS
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FORMULA
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G.f.: Sum_{k>0} binomial(k+2,2) * (-x)^k/(1 - x^k).
a(n) = Sum_{d|n} (-1)^d * binomial(d+2,2).
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MATHEMATICA
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a[n_] := DivisorSum[n, (-1)^#*Binomial[# + 2, 2] &]; Array[a, 50] (* Amiram Eldar, Jul 18 2023 *)
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PROG
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(PARI) a(n) = sumdiv(n, d, (-1)^d*binomial(d+2, 2));
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CROSSREFS
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KEYWORD
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sign,easy
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AUTHOR
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STATUS
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approved
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