OFFSET
1,15
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
EulerPhi(EulerPhi(15)) + 1 = EulerPhi(8) + 1 = 4 + 1 = 5, a prime; so a(15) = 2.
PROG
(PARI) a(n) = {nb = 1; n = eulerphi(n); while(! isprime(n+1), n = eulerphi(n); nb ++; ); return (nb); } \\ Michel Marcus, May 18 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Dec 26 2001
EXTENSIONS
Corrected and extended by Michel Marcus, May 18 2013
STATUS
approved