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 A359190 #13 Aug 27 2023 17:03:15
%S A359190 1,6,19,76,261,1074,4103,16536,65593,262686,1048587,4196644,16777229,
%T A359190 67117098,268436319,1073774896,4294967313,17180003478,68719476755,
%U A359190 274878432636,1099511640197,4398048608322,17592186044439,70368752620104,281474976711961,1125899940397134
%N A359190 a(n) = Sum_{d|n} d * 4^(n/d-1).
%F A359190 G.f.: Sum_{k>=1} k * x^k/(1 - 4 * x^k).
%F A359190 G.f.: Sum_{k>=1} 4^(k-1) * x^k/(1 - x^k)^2.
%t A359190 a[n_] := DivisorSum[n, 4^(n/#-1)*# &]; Array[a, 26] (* _Amiram Eldar_, Aug 27 2023 *)
%o A359190 (PARI) a(n) = sumdiv(n, d, d*4^(n/d-1));
%o A359190 (PARI) my(N=30, x='x+O('x^N)); Vec(sum(k=1, N, k*x^k/(1-4*x^k)))
%o A359190 (PARI) my(N=30, x='x+O('x^N)); Vec(sum(k=1, N, 4^(k-1)*x^k/(1-x^k)^2))
%Y A359190 Cf. A054599, A359189.
%K A359190 nonn,easy
%O A359190 1,2
%A A359190 _Seiichi Manyama_, Dec 19 2022