The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A046866 Numbers k such that 6*7^k - 1 is prime. 13
 0, 1, 2, 7, 18, 55, 69, 87, 119, 141, 189, 249, 354, 1586, 2135, 2865, 2930, 4214, 7167, 67485, 74402, 79326 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A003307, A002235, A046865, A079906, A001771, A005541, A056725, A046867, A079907. Sequence in context: A099626 A261331 A046672 * A291255 A294004 A214836 Adjacent sequences:  A046863 A046864 A046865 * A046867 A046868 A046869 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified January 22 10:25 EST 2020. Contains 331144 sequences. (Running on oeis4.)