A023239 Primes p such that 10*p + 7 is also prime.

3, 13, 19, 31, 61, 67, 79, 97, 109, 127, 163, 199, 223, 229, 241, 277, 283, 313, 367, 379, 421, 433, 439, 463, 487, 523, 541, 547, 571, 619, 631, 673, 691, 751, 757, 787, 811, 823, 829, 853, 859, 883, 937, 967, 1033, 1093, 1117, 1171, 1237, 1249, 1291, 1303, 1321

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Links

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

Crossrefs

Cf. A023238.

Subsequence of A102342.

Programs

Magma

[n: n in [0..1000] | IsPrime(n) and IsPrime(10*n+7)] // Vincenzo Librandi, Nov 20 2010

Mathematica

Select[Prime[Range[200]], PrimeQ[10# + 7] &] (* Alonso del Arte, Jun 24 2014 *)

Formula

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