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A308689
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a(n) = Sum_{d|n} d^(3*n/d - 2).
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3
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1, 3, 4, 21, 6, 216, 8, 1289, 2197, 8828, 12, 142278, 14, 526704, 1672464, 5246993, 18, 76887669, 20, 345319966, 1163085032, 2147498312, 24, 52918480178, 1220703151, 137438982060, 847293392440, 1374672048414, 30, 31838544112466, 32, 87962004029473
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OFFSET
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1,2
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LINKS
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FORMULA
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L.g.f.: -log(Product_{k>=1} (1 - k^3*x^k)^(1/k^3)) = Sum_{k>=1} a(k)*x^k/k.
a(p) = p+1 for prime p.
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MATHEMATICA
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a[n_] := DivisorSum[n, #^(3*n/# - 2) &]; Array[a, 32] (* Amiram Eldar, May 09 2021 *)
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PROG
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(PARI) {a(n) = sumdiv(n, d, d^(3*n/d-2))}
(PARI) N=66; x='x+O('x^N); Vec(x*deriv(-log(prod(k=1, N, (1-k^3*x^k)^(1/k^3)))))
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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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