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 A355116 #6 Jun 24 2022 08:30:48
%S A355116 1,1,4,13,43,124,388,1117,3370,9967,29860,88909,266896,798337,2394553,
%T A355116 7178233,21533029,64579750,193738672,581159161,1743472426,5230263235,
%U A355116 15690765067,47071824676,141215472685,423645012649,1270934954221,3812800839124,11438402333398,34315194788359
%N A355116 a(1) = 1; a(n+1) = Sum_{d|n} 3^(n/d - 1) * a(d).
%F A355116 G.f.: x * ( 1 + Sum_{n>=1} a(n) * x^n / (1 - 3 * x^n) ).
%F A355116 a(n) ~ 3^(n-1) / 2.
%t A355116 a[1] = 1; a[n_] := a[n] = Sum[3^((n - 1)/d - 1) a[d], {d, Divisors[n - 1]}]; Table[a[n], {n, 1, 30}]
%Y A355116 Cf. A003238, A351405, A355117.
%K A355116 nonn
%O A355116 1,3
%A A355116 _Ilya Gutkovskiy_, Jun 19 2022