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 A326400 #17 Jun 29 2023 13:22:11
%S A326400 0,1,0,2,1,3,0,5,0,7,1,6,0,8,3,10,1,9,0,15,0,13,1,15,5,14,0,16,1,21,0,
%T A326400 21,3,19,8,18,0,20,0,35,1,24,0,27,9,25,1,30,0,36,3,28,1,27,16,40,0,31,
%U A326400 1,45,0,32,0,42,14,39,0,39,3,56,1,45,0,38,15,40,8,42,0,71
%N A326400 Expansion of Sum_{k>=1} k * x^(2*k) / (1 - x^(3*k)).
%H A326400 Seiichi Manyama, <a href="/A326400/b326400.txt">Table of n, a(n) for n = 1..10000</a>
%F A326400 a(n) = Sum_{d|n, n/d==2 (mod 3)} d.
%F A326400 G.f.: Sum_{k>0} x^(3*k-1) / (1 - x^(3*k-1))^2. - _Seiichi Manyama_, Jun 29 2023
%t A326400 nmax = 80; CoefficientList[Series[Sum[k x^(2 k)/(1 - x^(3 k)), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
%t A326400 Table[DivisorSum[n, # &, MemberQ[{2}, Mod[n/#, 3]] &], {n, 1, 80}]
%Y A326400 Cf. A001822, A002131, A016789, A078182, A078708, A326399, A326401.
%Y A326400 Cf. A050464, A363900.
%K A326400 nonn
%O A326400 1,4
%A A326400 _Ilya Gutkovskiy_, Sep 11 2019