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 A363899 #18 Jun 29 2023 13:22:03
%S A363899 0,0,1,0,0,2,0,1,3,0,0,4,1,0,5,2,0,7,0,0,7,0,1,11,0,2,9,1,0,10,0,4,12,
%T A363899 0,0,14,0,1,16,5,0,14,1,0,15,2,0,23,0,0,17,4,1,21,0,9,19,1,0,20,0,0,
%U A363899 22,8,5,24,0,1,26,0,0,37,1,0,25,2,0,33,0,10,27,0,1,31,0,2,29,12,0
%N A363899 Expansion of Sum_{k>0} k * x^(3*k) / (1 - x^(5*k)).
%H A363899 Seiichi Manyama, <a href="/A363899/b363899.txt">Table of n, a(n) for n = 1..10000</a>
%F A363899 a(n) = Sum_{d|n, n/d==3 mod 5} d.
%F A363899 G.f.: Sum_{k>0} x^(5*k-2) / (1 - x^(5*k-2))^2.
%t A363899 a[n_] := DivisorSum[n, # &, Mod[n/#, 5] == 3 &]; Array[a, 100] (* _Amiram Eldar_, Jun 27 2023 *)
%o A363899 (PARI) a(n) = sumdiv(n, d, (n/d%5==3)*d);
%Y A363899 Cf. A363897, A363898, A363900.
%Y A363899 Cf. A001878, A284281.
%K A363899 nonn
%O A363899 1,6
%A A363899 _Seiichi Manyama_, Jun 27 2023