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A333752
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Sum of squarefree divisors of n that are <= sqrt(n).
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3
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1, 1, 1, 3, 1, 3, 1, 3, 4, 3, 1, 6, 1, 3, 4, 3, 1, 6, 1, 3, 4, 3, 1, 6, 6, 3, 4, 3, 1, 11, 1, 3, 4, 3, 6, 12, 1, 3, 4, 8, 1, 12, 1, 3, 9, 3, 1, 12, 8, 8, 4, 3, 1, 12, 6, 10, 4, 3, 1, 17, 1, 3, 11, 3, 6, 12, 1, 3, 4, 15, 1, 12, 1, 3, 9, 3, 8, 12, 1, 8, 4, 3, 1, 19, 6, 3, 4, 3, 1, 17
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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} mu(k)^2 * k * x^(k^2) / (1 - x^k).
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MATHEMATICA
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Table[DivisorSum[n, # &, # <= Sqrt[n] && SquareFreeQ[#] &], {n, 1, 90}]
nmax = 90; CoefficientList[Series[Sum[MoebiusMu[k]^2 k x^(k^2)/(1 - x^k), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
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PROG
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(PARI) a(n) = sumdiv(n, d, if ((d^2<=n) && issquarefree(d), d)); \\ Michel Marcus, Apr 03 2020
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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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