A158795 Primes of the form 2*7^k - 1.

13, 97, 4801, 33613, 1356446145697, 383162462761132828801, 6439811511626359453675213, 5303461691719306943558046763201, 1498096661930372466988988205389128987297, 81072431194288773664131732218033347601750444502024167492384908896001

Offset: 1

Author

Vincenzo Librandi, Mar 27 2009

Keywords

• nonn

Comments

Values of k are in A002959.

All terms are of the form 12*k + 1. - Altug Alkan, Sep 22 2018

Examples

			2*7^1 - 1 = 13, 2*7^2 - 1 = 97, and 2*7^4 - 1 = 4801 are primes, but 2*7^3 - 1 = 685 is not.
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..12

Crossrefs

Cf. A002959.

Programs

Magma

[a: n in [0..100] | IsPrime(a) where a is 2*7^n-1 ]; // Vincenzo Librandi, Jul 26 2012

Mathematica

Select[Table[2*7^n-1,{n,0,300}],PrimeQ] (* Vincenzo Librandi, Jul 26 2012 *)

PARI

for(k=1, 1e3, if(ispseudoprime(p=2*7^k-1), print1(p, ", "))); \\ Altug Alkan, Sep 22 2018

Extensions

a(7) corrected and examples edited by Jon E. Schoenfield, Jun 19 2010