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 A386745 #18 Aug 04 2025 08:44:45
%S A386745 0,1,20,90,336,650,1800,2450,5440,7371,13000,14762,30240,28730,49000,
%T A386745 58500,87296,83810,147420,130682,218400,220500,295240,280370,489600,
%U A386745 406875,574600,597780,823200,708122,1170000,924482,1397760,1328580,1676200,1592500,2476656
%N A386745 a(n) = n^2*sigma_2(n).
%H A386745 Vincenzo Librandi, <a href="/A386745/b386745.txt">Table of n, a(n) for n = 0..10000</a>
%F A386745 G.f.: Sum_{k>=1} k^4*x^k*(1 + x^k)/(1 - x^k)^3. - _Amiram Eldar_, Aug 01 2025
%F A386745 a(n) = n^2*A001157(n).
%F A386745 Dirichlet g.f.: zeta(s-2)*zeta(s-4). - _R. J. Mathar_, Aug 03 2025
%t A386745 Table[n^2*DivisorSigma[2, n], {n, 0, 40}]
%t A386745 nmax = 40; CoefficientList[Series[Sum[k^4*x^k*(1 + x^k)/(1 - x^k)^3, {k, 1, nmax}], {x, 0, nmax}], x]
%o A386745 (PARI) a(n) = if (n, n^2*sigma(n, 2), 0); \\ _Michel Marcus_, Aug 01 2025
%o A386745 (Magma) [0] cat [n^2*DivisorSigma(2, n): n in [1..45]]; // _Vincenzo Librandi_, Aug 04 2025
%Y A386745 Cf. A001157, A328259, A386746.
%K A386745 nonn,mult
%O A386745 0,3
%A A386745 _Vaclav Kotesovec_, Aug 01 2025