OFFSET
3,3
COMMENTS
Offset is 3 as a(1) and a(2) would be fractional. - Michel Marcus, Aug 13 2013
LINKS
Amiram Eldar, Table of n, a(n) for n = 3..10000
FORMULA
MATHEMATICA
EulerPhi[Prime[Range[3, 100]] - 1]/2 (* Amiram Eldar, Jan 12 2024 *)
PROG
(PARI) a(n) = eulerphi(eulerphi(prime(n)))/2; \\ Michel Marcus, Aug 13 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Matthijs Coster, Apr 29 2004
STATUS
approved