A005123 Numbers k such that 8k + 1 is prime.

2, 5, 9, 11, 12, 14, 17, 24, 29, 30, 32, 35, 39, 42, 44, 50, 51, 54, 56, 57, 65, 71, 72, 74, 75, 77, 80, 84, 95, 96, 101, 107, 110, 116, 117, 119, 122, 126, 129, 131, 137, 141, 144, 149, 150, 152, 156, 161, 162, 165, 170, 176, 179, 185, 186, 194, 200, 201

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

4*a(n) is the degree of the minimal polynomial of 2*cos(Pi/A007519(n)), called C(A007519(n), x) in A187360. - Wolfdieter Lang, Oct 24 2013

Links

• T. D. Noe, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A007519, A111174, A115249.

Programs

Magma

[n: n in [0..200] | IsPrime(8*n+1)]; // Vincenzo Librandi, Jun 25 2014

Mathematica

Select[Range[0, 300], PrimeQ[8 # + 1] &] (* Vincenzo Librandi, Jun 25 2014 *)

PARI

is(n)=isprime(8*n+1) \\ Charles R Greathouse IV, Apr 29 2015

Formula

a(n) = (A007519(n)-1)/8. - Zak Seidov, Sep 26 2007

Extensions

More terms from Wesley Ivan Hurt, Jun 25 2014