A079906 Numbers k such that 5*6^k - 1 is prime.

1, 2, 6, 7, 11, 23, 33, 48, 68, 79, 116, 151, 205, 1016, 1332, 1448, 3481, 3566, 3665, 11233, 13363, 29166, 44358, 58530, 191706, 386450, 605168, 616879, 1204077

Offset: 1

Author

Robert G. Wilson v, Jan 16 2003

Keywords

• nonn
• hard
• more

Comments

a(29) > 618000. - Karsten Bonath, Nov 04 2019

References

• R. K. Guy, Unsolved Problems in Theory of Numbers, Section A3.

Links

• H. C. Williams, The primality of certain integers of the form 2Ar^n - 1, Acta Arith. 39 (1981), 7-17.

Crossrefs

Cf. A003307, A002235, A046865, A046866, A001771, A005541, A056725, A046867, A079907, A247260.

Programs

Mathematica

Do[ If[ PrimeQ[5*6^n - 1], Print[n]], {n, 1, 5000}]

PARI

for(n=1,2000, if(isprime(5*6^n-1),print1(n, ", ")))

Extensions

a(20)-a(24) from Donovan Johnson, Nov 26 2008

a(25) from Robert Price, Jan 23 2016

a(26) from Karsten Bonath, Jul 01 2019

a(27) from Karsten Bonath, Oct 29 2019

a(28) from Karsten Bonath, Nov 04 2019

a(29) from Ryan Propper, Nov 21 2023