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 A364032 #14 Jul 03 2023 00:58:53
%S A364032 0,0,1,0,0,1,-1,0,1,0,1,1,0,-1,0,0,0,1,1,0,0,1,-1,1,0,0,2,-1,0,0,-1,0,
%T A364032 2,0,0,1,0,1,0,0,0,0,1,1,0,-1,-1,1,-1,0,2,0,0,2,0,-1,2,0,1,0,0,-1,-1,
%U A364032 0,0,2,1,0,0,0,-1,1,0,0,1,1,0,0,-1,0,2,0,1,0,0,1,0,1,0,0,0,-1,0,-1,0,1,0,-1,3,0,0
%N A364032 Expansion of Sum_{k>0} x^(3*k) / (1 + x^(4*k)).
%F A364032 G.f.: Sum_{k>0} (-1)^(k-1) * x^(4*k-1) / (1 - x^(4*k-1)).
%F A364032 a(n) = Sum_{d|n, d==3 (mod 4)} (-1)^((d-3)/4).
%t A364032 a[n_] := DivisorSum[n, (-1)^((# - 3)/4) &, Mod[#, 4] == 3 &]; Array[a, 100] (* _Amiram Eldar_, Jul 03 2023 *)
%o A364032 (PARI) a(n) = sumdiv(n, d, (d%4==3)*(-1)^((d-3)/4));
%Y A364032 Cf. A364033.
%K A364032 sign
%O A364032 1,27
%A A364032 _Seiichi Manyama_, Jul 01 2023