A068080 Integers n such that n + phi(n) is a prime.

1, 2, 3, 7, 15, 19, 31, 33, 35, 37, 51, 65, 69, 77, 79, 85, 91, 95, 97, 133, 139, 141, 143, 145, 157, 159, 161, 177, 187, 199, 209, 211, 213, 215, 217, 229, 235, 247, 255, 267, 271, 299, 303, 307, 319, 331, 335, 337, 339, 341, 345, 365, 367, 371, 379, 391, 393

Offset: 1

Author

Amarnath Murthy, Feb 17 2002

Keywords

• easy
• nonn

Comments

The subsequence of prime terms is given by A005382. - Michel Marcus, Aug 22 2015

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A050530.

Programs

Magma

[n: n in [1..400] |IsPrime(n+EulerPhi(n))]; // Vincenzo Librandi, Dec 19 2015

Mathematica

Select[Range[400], PrimeQ[# + EulerPhi[#]] &] (* Carl Najafi, Aug 22 2011 *)

PARI

isok(n) = isprime(n+eulerphi(n)); \\ Michel Marcus, Aug 22 2015

Extensions

Edited and extended by Robert G. Wilson v, Feb 18 2002