A112771 Semiprimes of the form 6n + 1.

25, 49, 55, 85, 91, 115, 121, 133, 145, 169, 187, 205, 217, 235, 247, 253, 259, 265, 289, 295, 301, 319, 355, 361, 391, 403, 415, 427, 445, 451, 469, 481, 493, 505, 511, 517, 529, 535, 553, 559, 565, 583, 589, 649, 655, 667, 679, 685, 697, 703, 721, 745

Offset: 1

Author

Jonathan Vos Post and Ray Chandler, Oct 15 2005

Keywords

• easy
• nonn

Comments

Union of A108164 and A108166.

Subsequence of A091300. - Zak Seidov, Dec 28 2015

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Programs

Magma

IsSemiprime:=func; [s: n in [2..150] | IsSemiprime(s) where s is 6*n + 1]; // Vincenzo Librandi, Sep 22 2012

Mathematica

Select[6 Range[0, 200] + 1, PrimeOmega[#] == 2&] (* Vincenzo Librandi, Sep 22 2012 *)

Formula

a(n) = 6 * A112775(n) +1.