A094051 a(n) = phi(phi(p))/2 where p = prime(n).

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

Author

Matthijs Coster, Apr 29 2004

Keywords

• nonn
• easy

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

Crossrefs

Cf. A000010, A000040, A008330, A023022.

Programs

Mathematica

EulerPhi[Prime[Range[3, 100]] - 1]/2 (* Amiram Eldar, Jan 12 2024 *)

PARI

a(n) = eulerphi(eulerphi(prime(n)))/2; \\ Michel Marcus, Aug 13 2013

Formula

From Amiram Eldar, Jan 12 2024: (Start)

a(n) = A008330(n)/2.

a(n) = A023022(A000040(n)-1). (End)