A049196 Squarefree numbers whose Euler totient function is also squarefree.

1, 2, 3, 6, 7, 11, 14, 22, 23, 31, 43, 46, 47, 59, 62, 67, 71, 79, 83, 86, 94, 103, 107, 118, 131, 134, 139, 142, 158, 166, 167, 179, 191, 206, 211, 214, 223, 227, 239, 262, 263, 278, 283, 311, 331, 334, 347, 358, 359, 367, 382, 383, 419, 422, 431, 439, 443, 446

Offset: 1

Author

Labos Elemer

Keywords

• nonn

Examples

			86 is here because it is squarefree and the same holds for phi(86) = 42.
		

Links

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

Crossrefs

A000010, A005117, A013929.

Programs

Magma

[n:n in [1..500]| IsSquarefree(n) and IsSquarefree(EulerPhi(n))]; // Marius A. Burtea, Jul 11 2019

Mathematica

Select[Range[500],And@@SquareFreeQ/@{#,EulerPhi[#]}&] (* Harvey P. Dale, Nov 05 2013 *)

PARI

isok(m) = issquarefree(m) && issquarefree(eulerphi(m)); \\ Michel Marcus, Jul 12 2019

Formula

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