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A094051
a(n) = phi(phi(p))/2 where p = prime(n).
1
1, 1, 2, 2, 4, 3, 5, 6, 4, 6, 8, 6, 11, 12, 14, 8, 10, 12, 12, 12, 20, 20, 16, 20, 16, 26, 18, 24, 18, 24, 32, 22, 36, 20, 24, 27, 41, 42, 44, 24, 36, 32, 42, 30, 24, 36, 56, 36, 56, 48, 32, 50, 64, 65, 66, 36, 44, 48, 46, 72, 48, 60, 48, 78, 40, 48, 86, 56, 80, 89, 60, 60, 54, 95, 96, 60
OFFSET
3,3
COMMENTS
Offset is 3 as a(1) and a(2) would be fractional. - Michel Marcus, Aug 13 2013
LINKS
FORMULA
From Amiram Eldar, Jan 12 2024: (Start)
a(n) = A008330(n)/2.
a(n) = A023022(A000040(n)-1). (End)
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