OFFSET
1,1
COMMENTS
2*prime(n)+1 is prime iff a(n) = 2*prime(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