A049197 - OEIS

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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

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OFFSET

1,1

COMMENTS

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

LINKS

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

EXAMPLE

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

MATHEMATICA

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

PROG