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A049197
Squarefree numbers whose Euler totient function is not squarefree.
1
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
1,1
COMMENTS
Numbers k such that abs(mu(k)) = 1 and mu(phi(k)) = 0.
LINKS
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
(PARI) isok(k) = issquarefree(k) && !issquarefree(eulerphi(k)); \\ Michel Marcus, Feb 12 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved