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 A363904 #17 Jun 29 2023 08:58:04 %S A363904 0,0,1,0,0,1,2,0,1,0,3,1,0,2,5,0,0,1,5,0,3,3,6,1,0,0,8,2,0,5,8,0,4,0, %T A363904 11,1,0,5,11,0,0,3,11,3,5,6,12,1,2,0,14,0,0,8,17,2,6,0,15,5,0,8,19,0, %U A363904 0,4,17,0,7,11,18,1,0,0,24,5,5,11,20,0,8,0,21,3,0,11,23,3,0,5,25,6 %N A363904 Expansion of Sum_{k>0} x^(3*k) / (1 - x^(4*k))^2. %H A363904 Seiichi Manyama, <a href="/A363904/b363904.txt">Table of n, a(n) for n = 1..10000</a> %F A363904 a(n) = (1/4) * Sum_{d|n, d==3 mod 4} (d+1) = (A001842(n) + A050452(n))/4. %F A363904 G.f.: Sum_{k>0} k * x^(4*k-1) / (1 - x^(4*k-1)). %t A363904 a[n_] := DivisorSum[n, # + 1 &, Mod[#, 4] == 3 &]/4; Array[a, 100] (* _Amiram Eldar_, Jun 27 2023 *) %o A363904 (PARI) a(n) = sumdiv(n, d, (d%4==3)*(d+1))/4; %Y A363904 Cf. A001842, A050452, A363903. %Y A363904 Cf. A113415, A363902. %K A363904 nonn %O A363904 1,7 %A A363904 _Seiichi Manyama_, Jun 27 2023