1,3

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.

Table of n, a(n) for n=1..69.

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

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

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

Cf. A225680 (denominators).

Sequence in context: A171233 A096907 A249146 * A081879 A066248 A065164

Adjacent sequences: A225676 A225677 A225678 * A225680 A225681 A225682

nonn,easy

Franz Vrabec, May 12 2013

approved