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%I #17 Feb 22 2021 12:04:27
%S 1,2,3,5,3,7,5,11,13,7,15,17,19,7,11,23,13,29,15,31,33,17,35,37,19,13,
%T 41,7,43,23,47,51,53,11,19,29,59,61,31,65,33,67,69,35,71,73,37,77,13,
%U 79,41,83,85,43,87,89,91,31,47,95,97,101,51,103,35,53,107
%N Denominators of phi(k)/k, as k runs through the squarefree numbers (A005117).
%C To every fraction taken by the arithmetical function m -> phi(m)/m there is exactly one n such that A225679(n)/A225680(n) is equal to it.
%H Ivan Neretin, <a href="/A225680/b225680.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n)=A005117(n)/gcd(A000010(A005117(n)),A005117(n)).
%e A005117(5)=6, phi(6)/6=2/6=1/3, so a(5)=3.
%t s = Select[Range[200], SquareFreeQ]; Denominator[EulerPhi[s]/s] (* _T. D. Noe_, May 13 2013 *)
%o (PARI) lista(nn) = apply(x->(denominator(eulerphi(x)/x)), Vec(select(issquarefree, [1..nn], 1))); \\ _Michel Marcus_, Feb 22 2021
%Y Cf. A225679 (numerators).
%K nonn,frac,easy
%O 1,2
%A _Franz Vrabec_, May 12 2013
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