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 A377507 #13 Oct 31 2024 11:23:08
%S A377507 1,1,2,12,66,690,4860,63000,711900,8876700,131405400,2160219600,
%T A377507 37553808600,686750664600,13805424032400,278759396916000,
%U A377507 6445702905642000,150985820419434000,3825993309462324000,99427990563910008000,2724045313186016820000,78032929885709378580000
%N A377507 Expansion of e.g.f. exp(Sum_{k>=1} phi(k)^2 * x^k/k), where phi is the Euler totient function A000010.
%H A377507 Vaclav Kotesovec, <a href="/A377507/b377507.txt">Table of n, a(n) for n = 0..435</a>
%F A377507 log(a(n)/n!) ~ 3 * c^(1/3) * n^(2/3) / 2^(2/3), where c = Product_{p primes} (1 - 2/p^2 + 1/p^3) = A065464 = 0.428249505677094440218765707581823546121298...
%t A377507 nmax = 25; $RecursionLimit->Infinity; a[n_]:=a[n]=If[n==0, 1, Sum[EulerPhi[k]^2*a[n-k], {k, 1, n}]/n];Table[a[n]*n!, {n, 0, nmax}]
%t A377507 nmax = 25; CoefficientList[Series[Exp[Sum[EulerPhi[k]^2 * x^k / k, {k, 1, nmax}]], {x, 0, nmax}], x] * Range[0, nmax]!
%Y A377507 Cf. A318917, A377508, A377509.
%Y A377507 Cf. A065464, A127473, A156302.
%K A377507 nonn
%O A377507 0,3
%A A377507 _Vaclav Kotesovec_, Oct 30 2024