A002959 Numbers k such that 2*7^k - 1 is prime.

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

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• hard
• more

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.

Programs

Mathematica

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

PARI

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

Extensions

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

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