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A079906 Numbers n such that 5*6^n -1 is prime. 15
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(27) > 4*10^5. - Karsten Bonath, Jul 01 2019

REFERENCES

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

LINKS

Table of n, a(n) for n=1..26.

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

MATHEMATICA

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

PROG

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

CROSSREFS

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

Sequence in context: A241720 A224082 A051678 * A226814 A233419 A189327

Adjacent sequences:  A079903 A079904 A079905 * A079907 A079908 A079909

KEYWORD

nonn,hard

AUTHOR

Robert G. Wilson v, Jan 16 2003

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

STATUS

approved

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Last modified October 19 14:36 EDT 2019. Contains 328222 sequences. (Running on oeis4.)