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 A359189 #12 Aug 27 2023 17:03:10
%S A359189 1,5,12,37,86,276,736,2261,6597,19870,59060,177780,531454,1595816,
%T A359189 4783272,14353429,43046738,129154113,387420508,1162301342,3486786672,
%U A359189 10460471356,31381059632,94143540948,282429536911,847289672390,2541865848120,7625600676808
%N A359189 a(n) = Sum_{d|n} d * 3^(n/d-1).
%F A359189 G.f.: Sum_{k>=1} k * x^k/(1 - 3 * x^k).
%F A359189 G.f.: Sum_{k>=1} 3^(k-1) * x^k/(1 - x^k)^2.
%t A359189 a[n_] := DivisorSum[n, 3^(n/#-1)*# &]; Array[a, 28] (* _Amiram Eldar_, Aug 27 2023 *)
%o A359189 (PARI) a(n) = sumdiv(n, d, d*3^(n/d-1));
%o A359189 (PARI) my(N=30, x='x+O('x^N)); Vec(sum(k=1, N, k*x^k/(1-3*x^k)))
%o A359189 (PARI) my(N=30, x='x+O('x^N)); Vec(sum(k=1, N, 3^(k-1)*x^k/(1-x^k)^2))
%Y A359189 Cf. A054599, A359190.
%K A359189 nonn,easy
%O A359189 1,2
%A A359189 _Seiichi Manyama_, Dec 19 2022