A023244 Primes that remain prime through 2 iterations of the function f(x) = 2x + 7.

2, 5, 17, 23, 53, 83, 137, 197, 227, 257, 293, 317, 347, 383, 467, 593, 647, 677, 683, 797, 857, 953, 1163, 1193, 1217, 1607, 1877, 1907, 1913, 1997, 2063, 2207, 2237, 2843, 2903, 3023, 3257, 3323, 3557, 3947, 4133, 4253, 4517, 4583, 4643, 4967, 5087, 5387

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Comments

Primes p such that 2*p+7 and 4*p+21 are also primes. - Vincenzo Librandi, Aug 04 2010

Links

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

Crossrefs

Subsequence of A023206 and A105760.

Programs

Magma

[n: n in [0..100000] | IsPrime(n) and IsPrime(2*n+7) and IsPrime(4*n+21)] // Vincenzo Librandi, Aug 04 2010

Mathematica

Select[Prime@ Range[10^3], Times @@ Boole@ PrimeQ@ NestList[2 # + 7 &, #, 2] > 0 &] (* Michael De Vlieger, Sep 12 2016 *)

Formula

a(n) == 5 (mod 6), for n > 1. - John Cerkan, Sep 12 2016