A023217 Primes p such that 5*p + 2 is also prime.

3, 7, 13, 19, 31, 61, 67, 73, 79, 97, 109, 151, 157, 181, 193, 199, 223, 313, 331, 349, 373, 397, 457, 487, 523, 541, 571, 577, 607, 613, 643, 661, 691, 709, 727, 739, 769, 811, 859, 919, 991, 997, 1021, 1033, 1039, 1069, 1087, 1129, 1171, 1201, 1213, 1249, 1279, 1321

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• easy

Comments

Except for the first term, all terms are congruent to 1 (mod 6). - John Cerkan, Sep 07 2016

Numbers k such that A280720(k) > 0. - Felix Fröhlich, Jan 07 2017

Intersection of A000040 and A111223. - Felix Fröhlich, Jan 07 2017

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000040, A111223, A280720. Subsequence of A111223.

Programs

Magma

[n: n in PrimesUpTo(400) | IsPrime(5*n+2)]; // Vincenzo Librandi, Nov 20 2010

Maple

A023217:=n->`if`(isprime(n) and isprime(5*n+2), n, NULL): seq(A023217(n), n=1..3*10^3); # Wesley Ivan Hurt, Sep 07 2016

Mathematica

Select[Prime[Range[200]], PrimeQ[5 # + 2] &] (* Vincenzo Librandi, May 20 2014 *)

PARI

is(n) = ispseudoprime(n) && ispseudoprime(5*n+2) \\ Felix Fröhlich, Jan 07 2017