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

1,1

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.

Links

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

Example

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

Mathematica

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

Prog

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

Crossrefs

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

Sequence in context: A356176 A343340 A280011 * A051488 A305613 A267967

Adjacent sequences: A175782 A175783 A175784 * A175786 A175787 A175788

Keyword

nonn

Author

Enrique Pérez Herrero, Sep 04 2010

Status

approved