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
(PARI) isok(k) = issquarefree(k) && !issquarefree(eulerphi(k)); \\ Michel Marcus, Feb 12 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved