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 A341639 #4 Feb 16 2021 21:18:14
%S A341639 1,1,2,6,19,95,291,2037,10203,71429,357240,3929640,19648533,255430929,
%T A341639 1788018540,16092167088,144829514049,2462101738833,17234712244012,
%U A341639 327459532636228,2947135794083881,38312765323095109,421440418557975839,9693129626833444297,87238166641520673597
%N A341639 a(1) = 1; a(n+1) = Sum_{d|n} phi(d) * a(d) * a(n/d).
%F A341639 a(1) = 1; a(n+1) = Sum_{k=1..n} a(gcd(n,k)) * a(n/gcd(n,k)).
%t A341639 a[1] = 1; a[n_] := a[n] = Sum[EulerPhi[d] a[d] a[(n - 1)/d], {d, Divisors[n - 1]}]; Table[a[n], {n, 25}]
%t A341639 a[1] = 1; a[n_] := a[n] = Sum[a[GCD[n - 1, k]] a[(n - 1)/GCD[n - 1, k]], {k, n - 1}]; Table[a[n], {n, 25}]
%Y A341639 Cf. A000010, A038044, A038045, A332791.
%K A341639 nonn
%O A341639 1,3
%A A341639 _Ilya Gutkovskiy_, Feb 16 2021