A120023 Numbers k such that 2*6^k + 1 is prime.

0, 1, 2, 3, 4, 10, 11, 17, 20, 28, 41, 48, 57, 58, 59, 71, 208, 972, 993, 1432, 2001, 2175, 2622, 3419, 3720, 4860, 7300, 7402, 14988, 15774, 18510, 22872, 52139, 77028, 149025, 172170, 239699

Offset: 1

Author

Pierre CAMI, Jun 04 2006

Keywords

• nonn
• more

Comments

If 6^n is of the form T(x,y) = 2xy+x+y [A083487] then 2*6^n+1 is not prime. - Vincenzo Librandi, Nov 13 2010

a(1)-a(37) proven prime by the primality proving program LLR. - Robert Price, Jan 08 2016

a(38) > 2.5*10^5. - Robert Price, Jan 08 2016

Crossrefs

Cf. A057472, A120024, A205771.

Programs

Mathematica

Select[Range[0, 2000], PrimeQ[2*6^# + 1] &] (* Vladimir Joseph Stephan Orlovsky, Jan 31 2012 *)

PARI

isok(n) = isprime(2*6^n+1); \\ Michel Marcus, Jan 08 2016

Extensions

More terms from Pierre CAMI, Jun 16 2006

a(32)-a(37) from Robert Price, Jan 08 2016