OFFSET
1,1
COMMENTS
Prime powers with sufficiently large exponents are in this sequence, including 8, 16, 32, 64, ..., 27, 81, ..., 25, 125.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
k such that abs(mu(k)) = 0 and abs(mu(phi(k))) = 0.
EXAMPLE
124 = 4*31 is in the sequence because phi(124)=60 and neither 124 nor 60 is squarefree.
MATHEMATICA
Select[Range[170], !SquareFreeQ[#] && !SquareFreeQ[EulerPhi[#]] &] (* Amiram Eldar, Jul 13 2019 *)
PROG
(PARI) isok(n) = !issquarefree(n) && ! issquarefree(eulerphi(n)); \\ Michel Marcus, Jul 13 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved