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 A308697 a(n) = Sum_{d|n} d^(3*d). 4
 1, 65, 19684, 16777281, 30517578126, 101559956688164, 558545864083284008, 4722366482869661990977, 58149737003040059690409853, 1000000000000000000030517578190, 23225154419887808141001767796309132, 708801874985091845381344408569542626596 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Seiichi Manyama, Table of n, a(n) for n = 1..152 FORMULA L.g.f.: -log(Product_{k>=1} (1 - x^k)^(k^(3*k-1))) = Sum_{k>=1} a(k)*x^k/k. G.f.: Sum_{k>=1} k^(3*k) * x^k/(1 - x^k). MATHEMATICA a[n_] := DivisorSum[n, #^(3*#) &]; Array[a, 12] (* Amiram Eldar, May 09 2021 *) PROG (PARI) {a(n) = sumdiv(n, d, d^(3*d))} (PARI) N=20; x='x+O('x^N); Vec(x*deriv(-log(prod(k=1, N, (1-x^k)^k^(3*k-1))))) (PARI) N=20; x='x+O('x^N); Vec(sum(k=1, N, k^(3*k)*x^k/(1-x^k))) CROSSREFS Column k=3 of A308698. Cf. A073706, A308757. Sequence in context: A264541 A323316 A120801 * A283580 A355496 A308491 Adjacent sequences:  A308694 A308695 A308696 * A308698 A308699 A308700 KEYWORD nonn AUTHOR Seiichi Manyama, Jun 17 2019 STATUS approved

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Last modified August 15 02:47 EDT 2022. Contains 356122 sequences. (Running on oeis4.)