A023243 Primes that remain prime through 2 iterations of the function f(x) = 2x + 5.

7, 13, 31, 37, 67, 73, 79, 139, 151, 181, 367, 541, 613, 661, 709, 739, 787, 811, 829, 997, 1087, 1117, 1123, 1249, 1327, 1669, 1753, 1801, 1861, 1999, 2011, 2113, 2179, 2239, 2293, 2473, 2557, 2659, 2713, 2719, 3037, 3181, 3187, 3271, 3301, 3517, 3727, 3793

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• easy

Comments

Primes p such that 2*p+5 and 4*p+15 are also primes. - Vincenzo Librandi, Aug 04 2010

Links

• John Cerkan, Table of n, a(n) for n = 1..10000

Crossrefs

Subsequence of A023205 and A089038.

Programs

Magma

[n: n in [0..100000] | IsPrime(n) and IsPrime(2*n+5) and IsPrime(4*n+15)] // Vincenzo Librandi, Aug 04 2010

PARI

is(n)=n%6==1 && isprime(2*n+5) && isprime(4*n+15) && isprime(n) \\ Charles R Greathouse IV, Sep 12 2016

Formula

a(n) == 1 (mod 6). - John Cerkan, Sep 12 2016