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 A370690 #8 Feb 27 2024 03:53:54
%S A370690 1,2,2,2,2,4,1,8,1,6,2,12,3,2,8,2,6,2,8,4,4,2,2,16,5,3,16,6,1,8,2,36,
%T A370690 8,18,4,18,18,16,2,24,2,8,5,4,2,2,2,60,3,10,8,7,9,32,4,8,32,3,8,48,5,
%U A370690 4,48,2,6,8,2,4,8,4,1,8,12,36,2,48,4,4,4,20,11
%N A370690 Denominator of sigma(phi(n))/phi(sigma(n)), where sigma is the sum of the divisors function and phi is the Euler totient function.
%C A370690 See A370689 for details.
%H A370690 Amiram Eldar, <a href="/A370690/b370690.txt">Table of n, a(n) for n = 1..10000</a>
%H A370690 Jean-Marie De Koninck and Florian Luca, <a href="https://eudml.org/doc/284003">On the composition of the Euler function and the sum of divisors function</a>, Colloquium Mathematicum, Vol. 108, No. 1 (2007), pp. 31-51.
%t A370690 Table[DivisorSigma[1, EulerPhi[n]]/EulerPhi[DivisorSigma[1, n]], {n, 1, 100}] // Denominator
%o A370690 (PARI) a(n) = {my(f = factor(n)); denominator(sigma(eulerphi(f)) / eulerphi(sigma(f)));}
%Y A370690 Cf. A000010, A000203, A033632, A062401, A062402, A065395, A066930 (positions of 1's), A073858, A289336, A289412, A370689 (numerators).
%K A370690 nonn,easy,frac
%O A370690 1,2
%A A370690 _Amiram Eldar_, Feb 27 2024