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A348660
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a(n) = Sum_{d|n, d <= sqrt(n)} (-1)^(n/d + 1) * d.
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4
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1, -1, 1, -3, 1, 1, 1, -3, 4, 1, 1, -6, 1, 1, 4, -7, 1, -2, 1, 1, 4, 1, 1, -10, 6, 1, 4, 1, 1, -7, 1, -7, 4, 1, 6, -8, 1, 1, 4, -12, 1, 4, 1, 1, 9, 1, 1, -16, 8, -4, 4, 1, 1, 4, 6, -14, 4, 1, 1, -13, 1, 1, 11, -15, 6, 4, 1, 1, 4, -11, 1, -8, 1, 1, 9, 1, 8, 4, 1, -20
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OFFSET
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1,4
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LINKS
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FORMULA
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G.f.: Sum_{k>=1} (-1)^(k + 1) * k * x^(k^2) / (1 + x^k).
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MATHEMATICA
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Table[DivisorSum[n, (-1)^(n/# + 1) # &, # <= Sqrt[n] &], {n, 1, 80}]
nmax = 80; CoefficientList[Series[Sum[(-1)^(k + 1) k x^(k^2)/(1 + x^k), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
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PROG
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CROSSREFS
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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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