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A363700
a(n) = phi(2*prime(n)+1).
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
1,1
COMMENTS
2*prime(n)+1 is prime iff a(n) = 2*prime(n).
FORMULA
a(n) = A000010(A072055(n)).
a(n) = A037225(A000040(n)).
MATHEMATICA
a[n_] := EulerPhi[2*Prime[n] + 1]; Array[a, 100] (* Amiram Eldar, Jun 16 2023 *)
PROG
(PARI) a(n)=eulerphi(2*prime(n)+1)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alain Rocchelli, Jun 16 2023
STATUS
approved