OFFSET
1,3
COMMENTS
a(23) > 2*10^5. - Robert Price, Nov 13 2015
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, Section A3.
LINKS
H. C. Williams, The primality of certain integers of the form 2Ar^n - 1, Acta Arith. 39 (1981), 7-17.
MATHEMATICA
Do[ If[ PrimeQ[6*7^n - 1], Print[n]], {n, 0, 5650}]
PROG
(PARI) for(n=0, 2000, if(isprime(6*7^n-1), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
EXTENSIONS
One more term from Jason Earls, Jul 21 2001
More terms from Robert G. Wilson v, Jan 17 2003
One more term from Ryan Propper, Jun 05 2006
a(20)-a(22) from Donovan Johnson, Nov 26 2008
First term 0 inserted by Georg Fischer, Aug 01 2019
STATUS
approved