1,2

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.

Ivan Neretin, Table of n, a(n) for n = 1..10000

a(n)=A005117(n)/gcd(A000010(A005117(n)),A005117(n)).

A005117(5)=6, phi(6)/6=2/6=1/3, so a(5)=3.

s = Select[Range[200], SquareFreeQ]; Denominator[EulerPhi[s]/s] (* T. D. Noe, May 13 2013 *)

Cf. A225679 (numerators).

Sequence in context: A117366 A073482 A318411 * A107685 A161984 A125677

Adjacent sequences: A225677 A225678 A225679 * A225681 A225682 A225683

nonn,easy

Franz Vrabec, May 12 2013

approved