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 A363900 #18 Jun 29 2023 11:22:43
%S A363900 0,0,0,1,0,0,0,2,1,0,0,3,0,1,0,4,0,2,1,5,0,0,0,7,0,0,3,9,1,0,0,8,0,1,
%T A363900 0,13,0,2,1,10,0,3,0,12,5,0,0,14,1,0,0,13,0,7,0,18,3,2,1,15,0,0,7,17,
%U A363900 0,0,0,19,1,5,0,29,0,1,0,23,0,2,1,20,9,0,0,28,0,0,3,24,1,10,0,23,0,1,5,28,0
%N A363900 Expansion of Sum_{k>0} k * x^(4*k) / (1 - x^(5*k)).
%H A363900 Seiichi Manyama, <a href="/A363900/b363900.txt">Table of n, a(n) for n = 1..10000</a>
%F A363900 a(n) = Sum_{d|n, n/d==4 mod 5} d.
%F A363900 G.f.: Sum_{k>0} x^(5*k-1) / (1 - x^(5*k-1))^2.
%t A363900 a[n_] := DivisorSum[n, # &, Mod[n/#, 5] == 4 &]; Array[a, 100] (* _Amiram Eldar_, Jun 27 2023 *)
%o A363900 (PARI) a(n) = sumdiv(n, d, (n/d%5==4)*d);
%Y A363900 Cf. A363897, A363898, A363899.
%Y A363900 Cf. A001899, A284103.
%K A363900 nonn
%O A363900 1,8
%A A363900 _Seiichi Manyama_, Jun 27 2023