A363700 a(n) = phi(2*prime(n)+1).

4, 6, 10, 8, 22, 18, 24, 24, 46, 58, 36, 40, 82, 56, 72, 106, 96, 80, 72, 120, 84, 104, 166, 178, 96, 168, 132, 168, 144, 226, 128, 262, 200, 180, 264, 200, 144, 216, 264, 346, 358, 220, 382, 252, 312, 216, 276, 296, 288, 288, 466, 478, 264, 502, 408, 480, 420, 360, 288, 562

Offset: 1

Author

Alain Rocchelli, Jun 16 2023

Keywords

• nonn

Comments

2*prime(n)+1 is prime iff a(n) = 2*prime(n).

Crossrefs

Cf. A000010, A000040, A008331, A037225, A072055.

Programs

Mathematica

a[n_] := EulerPhi[2*Prime[n] + 1]; Array[a, 100] (* Amiram Eldar, Jun 16 2023 *)

PARI

a(n)=eulerphi(2*prime(n)+1)

Formula

a(n) = A000010(A072055(n)).

a(n) = A037225(A000040(n)).