A356437 a(n) = n! * Sum_{k=1..n} sigma_k(k)/k.
1, 7, 77, 1946, 84754, 6202524, 636369348, 89979720144, 16431405256656, 3796658174518560, 1077102230236529760, 368915006390671969920, 149873555740938949215360, 71297150722148582901815040, 39244301012876892023553235200
Offset: 1
Keywords
Programs
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Mathematica
Table[n! * Sum[DivisorSigma[k, k]/k, {k, 1, n}], {n, 1, 20}] (* Vaclav Kotesovec, Aug 07 2022 *) -
PARI
a(n) = n!*sum(k=1, n, sigma(k, k)/k);
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PARI
my(N=20, x='x+O('x^N)); Vec(serlaplace(-sum(k=1, N, log(1-(k*x)^k)/k)/(1-x)))
Formula
E.g.f.: -(1/(1-x)) * Sum_{k>0} log(1 - (k*x)^k)/k.
a(n) ~ n! * n^(n-1). - Vaclav Kotesovec, Aug 07 2022