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A175785
Numbers n such that the number of distinct prime divisors of n does not divide phi(n).
2
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
KEYWORD
nonn
AUTHOR
STATUS
approved