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 A332791 #11 May 09 2021 08:06:51
%S A332791 1,1,2,5,12,49,104,625,2512,15077,60358,603581,2414438,28973257,
%T A332791 173840168,1390721397,11125773688,178012379009,1068074289230,
%U A332791 19225337206141,153802697709496,1845632372514581,18456323725749392,406039121966486625,3248312975734309938
%N A332791 a(1) = 1; a(n+1) = Sum_{d|n} phi(d) * a(d).
%H A332791 Vaclav Kotesovec, <a href="/A332791/b332791.txt">Table of n, a(n) for n = 1..495</a>
%F A332791 a(1) = 1; a(n+1) = Sum_{k=1..n} a(n/gcd(n, k)).
%F A332791 a(n) = Sum_{k=1..n} a(gcd(n,k))*phi(gcd(n,k))/phi(n/gcd(n,k)). - _Richard L. Ollerton_, May 07 2021
%t A332791 a[1] = 1; a[n_] := Sum[EulerPhi[d] a[d], {d, Divisors[n - 1]}]; Table[a[n], {n, 1, 25}]
%t A332791 a[1] = 1; a[n_] := a[n] = Sum[a[(n - 1)/GCD[n - 1, k]], {k, 1, n - 1}]; Table[a[n], {n, 1, 25}]
%Y A332791 Cf. A000010, A006874, A038045, A057660, A307793, A307794, A332792.
%K A332791 nonn
%O A332791 1,3
%A A332791 _Ilya Gutkovskiy_, Feb 24 2020