A175785 Numbers n such that the number of distinct prime divisors of n does not divide phi(n).

30, 60, 66, 102, 110, 120, 132, 138, 150, 165, 170, 174, 204, 220, 230, 240, 246, 255, 264, 276, 282, 290, 300, 318, 340, 345, 348, 354, 374, 408, 410, 426, 435, 440, 460, 470, 480, 492, 498, 506, 528, 530, 534, 550, 552, 561, 564, 580, 590, 600, 606, 615

Offset: 1

Author

Enrique Pérez Herrero, Sep 04 2010

Keywords

• nonn

Comments

a(n) gives the integers where omega(n) = A001221(n) does not divide phi(n) = A000010(n).

This sequence does not contain any prime powers (A000961), nor any numbers with only two distinct prime divisors (A007774); so it is a subsequence of A000977.

Examples

			30 is in this sequence because omega(30)=3 does not divide phi(30)=8.
		

Links

• Enrique Pérez Herrero, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001221, A000010, A075592, A109425, A109427, A192218, A000977, A000961, A007774.

Programs

Mathematica

Select[Range[2,700],Mod[EulerPhi[#],PrimeNu[#]]!=0&] (* Harvey P. Dale, Dec 29 2019 *)

PARI

isok(n) = (eulerphi(n) % omega(n) != 0) \\ Michel Marcus, Jun 12 2013