OFFSET
1,1
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..39340
EXAMPLE
phi(20)+1 = 8+1 = 9 is not prime.
MATHEMATICA
Select[Range[200], !PrimeQ[EulerPhi[#]+1]&] (* Harvey P. Dale, Aug 31 2018 *)
PROG
(PARI) isok(k) = !isprime(eulerphi(k)+1); \\ Michel Marcus, Jun 28 2021
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
Name edited by Antti Karttunen, Dec 05 2017
STATUS
approved