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A363583
Numbers k such that 2*phi(k)+k is a prime, where phi is A000010.
0
1, 3, 5, 7, 11, 13, 15, 23, 33, 35, 37, 43, 47, 53, 61, 67, 69, 71, 77, 87, 95, 103, 113, 119, 123, 127, 133, 137, 143, 159, 163, 167, 177, 181, 191, 193, 209, 211, 217, 249, 251, 257, 259, 263, 267, 271, 277, 293, 299, 307, 313, 329, 331, 335, 337, 339
OFFSET
1,2
COMMENTS
All the terms are odd squarefree numbers.
MATHEMATICA
Select[Range[1, 350, 2], PrimeQ[2*EulerPhi[#] + #] &] (* Amiram Eldar, Aug 17 2023 *)
PROG
(Python)
from sympy import totient, isprime
print([k for k in range(1, 340) if isprime(2*totient(k) + k)])
(PARI) isok(k) = isprime(k+2*eulerphi(k)); \\ Michel Marcus, Aug 20 2023
CROSSREFS
Subsequence of A056911.
Subsequence: A088878 (the prime terms).
Sequence in context: A247648 A117203 A081118 * A355918 A003255 A263321
KEYWORD
nonn,easy
AUTHOR
Darío Clavijo, Aug 17 2023
STATUS
approved