This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A356323 #15 Aug 07 2022 04:44:41 %S A356323 1,11,89,794,6994,72204,753108,8973264,111281616,1524322080, %T A356323 21601104480,340803192960,5483287025280,96044874750720, %U A356323 1748238132614400,34093033838438400,682396164763084800,14706429413353574400,323342442475011993600,7585740483060676608000 %N A356323 a(n) = n! * Sum_{k=1..n} sigma_3(k)/k. %F A356323 E.g.f.: (1/(1-x)) * Sum_{k>0} x^k * (1 + x^k)/(k * (1 - x^k)^3). %F A356323 E.g.f.: -(1/(1-x)) * Sum_{k>0} k^2 * log(1 - x^k). %F A356323 a(n) ~ n! * Pi^4 * n^3 / 270. - _Vaclav Kotesovec_, Aug 07 2022 %t A356323 Table[n! * Sum[DivisorSigma[3, k]/k, {k, 1, n}], {n, 1, 20}] (* _Vaclav Kotesovec_, Aug 07 2022 *) %o A356323 (PARI) a(n) = n!*sum(k=1, n, sigma(k, 3)/k); %o A356323 (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(sum(k=1, N, x^k*(1+x^k)/(k*(1-x^k)^3))/(1-x))) %o A356323 (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(-sum(k=1, N, k^2*log(1-x^k))/(1-x))) %Y A356323 Cf. A001158, A064603, A356010, A356297, A356298. %K A356323 nonn %O A356323 1,2 %A A356323 _Seiichi Manyama_, Aug 03 2022