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 A364044 #11 Jul 03 2023 11:45:04
%S A364044 0,1,0,1,0,1,-1,1,0,1,0,2,0,0,0,1,-1,1,0,1,-1,2,0,2,0,1,-1,0,0,1,0,2,
%T A364044 0,0,-1,2,-1,1,0,1,0,1,0,2,0,1,-1,2,-1,1,-1,2,0,0,0,0,-1,1,0,2,0,2,-1,
%U A364044 2,0,2,-1,0,0,0,0,3,0,0,0,1,-2,1,0,1,-1,2,0,2,-1,1,-1,2,0,1,-1,2,0,0,0,3,-1,0,0,1
%N A364044 Expansion of Sum_{k>0} x^(2*k) / (1 + x^(5*k)).
%F A364044 G.f.: Sum_{k>0} (-1)^(k-1) * x^(5*k-3) / (1 - x^(5*k-3)).
%F A364044 a(n) = Sum_{d|n, d==2 (mod 5)} (-1)^d.
%t A364044 a[n_] := DivisorSum[n, (-1)^# &, Mod[#, 5] == 2 &]; Array[a, 100] (* _Amiram Eldar_, Jul 03 2023 *)
%o A364044 (PARI) a(n) = sumdiv(n, d, (d%5==2)*(-1)^d);
%Y A364044 Cf. A364043, A364045, A364046.
%Y A364044 Cf. A001877, A364020.
%K A364044 sign
%O A364044 1,12
%A A364044 _Seiichi Manyama_, Jul 03 2023