A139392 Odd noncyclic numbers; odd numbers n such that gcd(n,phi(n)) > 1.

9, 21, 25, 27, 39, 45, 49, 55, 57, 63, 75, 81, 93, 99, 105, 111, 117, 121, 125, 129, 135, 147, 153, 155, 165, 169, 171, 175, 183, 189, 195, 201, 203, 205, 207, 219, 225, 231, 237, 243, 245, 253, 261, 273, 275, 279, 285, 289, 291, 297, 301, 305, 309, 315, 325

Offset: 1

Author

T. D. Noe, Apr 17 2008

Keywords

• nonn

Comments

Sequence A060679 lists all noncyclic numbers, which includes all even numbers >2.

Links

• T. D. Noe, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A003277 (cyclic numbers).

Programs

Mathematica

Select[Range[1,400,2], GCD[ #,EulerPhi[ # ]]>1&]

PARI

is(n)=n%2 && gcd(eulerphi(n),n)>1 \\ Charles R Greathouse IV, Aug 23 2017