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

1,1

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

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 *)

Prog

(Magma) [n: n in PrimesUpTo(400) | IsPrime(5*n+2)]; // Vincenzo Librandi, Nov 20 2010
(PARI) is(n) = ispseudoprime(n) && ispseudoprime(5*n+2) \\ Felix Fröhlich, Jan 07 2017

Crossrefs

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

Sequence in context: A023237 A106061 A155703 * A106077 A216515 A048977

Adjacent sequences: A023214 A023215 A023216 * A023218 A023219 A023220

Keyword

nonn,easy

Author

David W. Wilson

Status

approved