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 A366135 #36 Dec 15 2023 06:19:52
%S A366135 1,11,33,98,140,366,371,820,936,1550,1397,3276,2288,4102,4650,6696,
%T A366135 5066,10413,7049,13860,12306,15422,12443,27480,17825,25246,25650,
%U A366135 36652,24824,51900,30287,54096,46266,55862,52150,93366,51356,77710,75738,116200,69782,137172
%N A366135 Expansion of Sum_{k>=1} k^3 * x^k/(1 - x^k)^3.
%H A366135 Amiram Eldar, <a href="/A366135/b366135.txt">Table of n, a(n) for n = 1..10000</a>
%F A366135 a(n) = n * (n * sigma(n) + sigma_2(n))/2.
%F A366135 a(n) = Sum_{d|n} d^3 * binomial(n/d+1,2).
%F A366135 a(n) = Sum_{k=1..n} k*sigma_2(gcd(n,k)).
%F A366135 Sum_{k=1..n} a(k) ~ (Pi^2/48 + zeta(3)/8) * n^4. - _Amiram Eldar_, Dec 15 2023
%t A366135 a[n_] := (n * DivisorSigma[1, n] + DivisorSigma[2, n]) * n/2; Array[a, 50] (* _Amiram Eldar_, Dec 15 2023 *)
%o A366135 (PARI) a(n) = n*(n*sigma(n)+sigma(n, 2))/2;
%Y A366135 Cf. A007437, A309731, A309732.
%Y A366135 Cf. A001158, A328259.
%Y A366135 Cf. A000203, A001157.
%K A366135 nonn,easy
%O A366135 1,2
%A A366135 _Seiichi Manyama_, Oct 28 2023