OFFSET
1,1
COMMENTS
Values of k are in A002959.
All terms are of the form 12*k + 1. - Altug Alkan, Sep 22 2018
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..12
EXAMPLE
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.
MATHEMATICA
Select[Table[2*7^n-1, {n, 0, 300}], PrimeQ] (* Vincenzo Librandi, Jul 26 2012 *)
PROG
(Magma) [a: n in [0..100] | IsPrime(a) where a is 2*7^n-1 ]; // Vincenzo Librandi, Jul 26 2012
(PARI) for(k=1, 1e3, if(ispseudoprime(p=2*7^k-1), print1(p, ", "))); \\ Altug Alkan, Sep 22 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Vincenzo Librandi, Mar 27 2009
EXTENSIONS
a(7) corrected and examples edited by Jon E. Schoenfield, Jun 19 2010
STATUS
approved