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A359198
Numbers k such that 2*phi(k)-k is a prime, where phi is A000010.
0
5, 7, 9, 13, 19, 21, 31, 33, 35, 43, 45, 51, 61, 65, 69, 73, 75, 77, 85, 91, 103, 109, 115, 119, 123, 133, 139, 141, 143, 145, 151, 161, 181, 185, 193, 199, 209, 213, 221, 229, 241, 249, 259, 265, 271, 283, 285, 287, 299, 303, 313, 319, 321, 329, 335, 339
OFFSET
1,1
COMMENTS
All terms of this sequence are odd. - Saish S. Kambali, Aug 16 2023
MATHEMATICA
primeQ[n_] := n > 0 && PrimeQ[n]; Select[Range[1, 350, 2], primeQ[2*EulerPhi[#] - #] &] (* Amiram Eldar, Aug 16 2023 *)
PROG
(Python)
from sympy import totient, isprime
print([n for n in range(1, 340) if isprime(2 * totient(n) - n)])
(PARI) isok(k) = isprime(2*eulerphi(k)-k); \\ Michel Marcus, Sep 13 2023
CROSSREFS
Subsequence: A006512 (the prime terms).
Sequence in context: A050550 A079523 A231271 * A039504 A097280 A155732
KEYWORD
nonn,easy
AUTHOR
Darío Clavijo, Aug 16 2023
STATUS
approved