OFFSET
1,2
COMMENTS
a(n) is prime only for a(2)=2, for other cases: eulerphi(p) = p-1 = n^3, and p = 1 + n^3 = (n+1)(n^2-n+1), so p cannot be a prime. - Enrique Pérez Herrero, Aug 29 2010
A013730 is a subsequence. - Enrique Pérez Herrero, Aug 29 2010
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..2500 from E. Pérez Herrero)
EXAMPLE
phi(247) = 216 = 6*6*6.
MATHEMATICA
Select[ Range[ 2000 ], IntegerQ[ Power[ EulerPhi[ # ], 1/3 ] ]& ]
PROG
(PARI) for(n=1, 1e4, if(ispower(eulerphi(n), 3), print1(n", "))) \\ Charles R Greathouse IV, Jul 31 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved