A049197 Squarefree numbers whose Euler totient function is not squarefree.

5, 10, 13, 15, 17, 19, 21, 26, 29, 30, 33, 34, 35, 37, 38, 39, 41, 42, 51, 53, 55, 57, 58, 61, 65, 66, 69, 70, 73, 74, 77, 78, 82, 85, 87, 89, 91, 93, 95, 97, 101, 102, 105, 106, 109, 110, 111, 113, 114, 115, 119, 122, 123, 127, 129, 130, 133, 137, 138, 141, 143

Offset: 1

Author

Labos Elemer

Keywords

• nonn

Comments

Numbers k such that abs(mu(k)) = 1 and mu(phi(k)) = 0.

Examples

			110 = 2*5*11 is squarefree but phi(110) = 40 is divisible by a square, so 110 is in the sequence.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A005117, A013929, A049195, A049196.

Programs

Mathematica

Select[Range[144], SquareFreeQ[#] && !SquareFreeQ[EulerPhi[#]] &] (* Amiram Eldar, Feb 12 2021 *)

PARI

isok(k) = issquarefree(k) && !issquarefree(eulerphi(k)); \\ Michel Marcus, Feb 12 2021