A143826 Numbers k such that 6*k^2 - 1 is prime.

1, 2, 3, 5, 7, 8, 10, 12, 13, 17, 20, 22, 27, 28, 30, 32, 35, 38, 43, 45, 52, 55, 58, 60, 62, 63, 65, 68, 70, 73, 75, 77, 82, 83, 87, 93, 97, 100, 102, 115, 120, 122, 130, 132, 143, 150, 153, 168, 173, 177, 187, 193, 197, 200, 207, 208, 210, 212, 220, 222, 223, 225

Offset: 1

Author

Artur Jasinski, Sep 02 2008

Keywords

• nonn
• changed

Crossrefs

Cf. A090686.

Programs

Mathematica

p = 6; a = {}; Do[k = p x^2 - 1; If[PrimeQ[k], AppendTo[a, x]], {x, 1, 1000}]; a
Select[Range[250],PrimeQ[6#^2-1]&] (* Harvey P. Dale, Apr 22 2012 *)

PARI

is(n)=isprime(6*n^2-1) \\ Charles R Greathouse IV, Feb 17 2017