

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
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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

Table of n, a(n) for n=1..22.
H. C. Williams, The primality of certain integers of the form 2Ar^n  1, Acta Arith. 39 (1981), 717.


MATHEMATICA

Do[ If[ PrimeQ[6*7^n  1], Print[n]], {n, 0, 5650}]


PROG

(PARI) for(n=0, 2000, if(isprime(6*7^n1), 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

N. J. A. Sloane


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



