A106630 Numbers k such that (prime(k)^2 - 1)/6 - prime(k) is prime.

7, 8, 12, 13, 17, 20, 24, 25, 28, 29, 32, 39, 42, 45, 52, 53, 58, 59, 63, 64, 67, 72, 75, 79, 83, 87, 88, 93, 100, 102, 114, 115, 125, 126, 127, 131, 139, 140, 144, 154, 159, 160, 173, 180, 190, 195, 219, 223, 232, 234, 240, 248, 253, 265, 278, 279, 284, 296, 299

Offset: 1

Author

Pierre CAMI, May 11 2005

Keywords

• nonn

Examples

			(17^2 -1)/6 - 17 = 48 - 17 = 31 is prime, 17=prime(7), so 7 is a term.
		

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A084922.

Programs

Mathematica

Select[Range[350], PrimeQ[(Prime[#]^2 -6*Prime[#] -1)/6] &] (* G. C. Greubel, Sep 08 2021 *)

PARI

is(n,p=prime(n))=isprime((p^2-1)/6-p) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(12) corrected by R. J. Mathar, Nov 13 2009