A002959 - OEIS

%I M0979 #31 Oct 21 2023 23:47:12

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

%T 147454,174180

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

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

%D 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.

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

%o (PARI) is(n)=ispseudoprime(2*7^n-1) \\ _Charles R Greathouse IV_, Feb 17 2017

%K nonn,hard,more

%O 1,2

%A _N. J. A. Sloane_

%E More terms from _Robert G. Wilson v_, Jan 05 2001

%E a(14)-a(19) from _Predrag Kurtovic_, May 24 2015