A002959 Numbers k such that 2*7^k - 1 is prime. (Formerly M0979)

1, 2, 4, 5, 14, 24, 29, 36, 46, 80, 474, 1018, 5180, 22581, 41649, 52744, 114564, 147454, 174180

Offset

1,2

References

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

C. R. Zarnke and H. C. Williams, Computer determination of some large primes, pp. 563-570 in Proceedings of the Louisiana Conference on Combinatorics, Graph Theory and Computer Science. Vol. 2, edited R. C. Mullin et al., 1971.

Links

Table of n, a(n) for n=1..19.

Mathematica

Do[ If[ PrimeQ[ 2*7^n - 1 ], Print[n] ], {n, 1, 10000} ]

Prog

(PARI) is(n)=ispseudoprime(2*7^n-1) \\ Charles R Greathouse IV, Feb 17 2017

Crossrefs

Sequence in context: A182375 A295402 A121410 * A306919 A295031 A178436

Adjacent sequences: A002956 A002957 A002958 * A002960 A002961 A002962

Keyword

nonn,hard,more

Author

N. J. A. Sloane

Extensions

More terms from Robert G. Wilson v, Jan 05 2001

a(14)-a(19) from Predrag Kurtovic, May 24 2015

Status

approved