OFFSET
1,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
EXAMPLE
Large primes belong to this set. Composites like: n=35 has 2 prime divisors, Phi(35)=24 Pi(35)=11; In reduced residue system 9 primes and 15 nonprimes occur.
MATHEMATICA
Select[Range[500], 2*PrimePi[#] - 2*PrimeNu[#] < EulerPhi[#] &] (* G. C. Greubel, May 12 2017 *)
PROG
(PARI) isok(n) = 2*(primepi(n) - omega(n)) < eulerphi(n); \\ Michel Marcus, May 13 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved