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A348953
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a(n) = -Sum_{d|n, d < sqrt(n)} (-1)^(d + n/d) * d.
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4
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0, 1, -1, 1, -1, 3, -1, -1, -1, 3, -1, 2, -1, 3, -4, -1, -1, 6, -1, 3, -4, 3, -1, -2, -1, 3, -4, 3, -1, 11, -1, -5, -4, 3, -6, 6, -1, 3, -4, 0, -1, 12, -1, 3, -9, 3, -1, -8, -1, 8, -4, 3, -1, 12, -6, 2, -4, 3, -1, 5, -1, 3, -11, -5, -6, 12, -1, 3, -4, 15, -1, 0, -1, 3, -9, 3, -8, 12, -1, -8
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OFFSET
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1,6
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LINKS
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FORMULA
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G.f.: Sum_{k>=1} k * x^(k*(k + 1)) / (1 + x^k).
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MATHEMATICA
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Table[-DivisorSum[n, (-1)^(# + n/#) # &, # < Sqrt[n] &], {n, 1, 80}]
nmax = 80; CoefficientList[Series[Sum[k x^(k (k + 1))/(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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Cf. A000593, A046897, A070039, A109506, A333810, A348608, A348951, A348952, A348954, A348955, A348956.
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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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