A174100 Numbers k such that both 2*k + 1 and 6*k + 1 are prime.

1, 2, 3, 5, 6, 11, 18, 21, 23, 26, 30, 33, 35, 51, 56, 63, 68, 81, 83, 90, 95, 96, 105, 125, 128, 131, 135, 138, 146, 153, 156, 165, 168, 173, 186, 200, 215, 216, 221, 230, 233, 243, 245, 261, 270, 278, 293, 296, 300, 336, 338, 363, 375, 378, 380, 398

Offset: 1

Author

Juri-Stepan Gerasimov, Mar 07 2010

Keywords

• nonn

Examples

			a(1)=1 because 1*2 + 1 = 3 (a prime) and 1*6 + 1 = 7 (also a prime).
		

Crossrefs

Cf. A002476, A065091.

Programs

Mathematica

Select[Range[400],PrimeQ[2#+1]&&PrimeQ[6#+1]&]  (* Harvey P. Dale, Jan 17 2011 *)

Extensions

Corrected (118 removed, 132 replaced by 131) by R. J. Mathar, Apr 20 2010

Name edited by Jon E. Schoenfield, May 19 2019