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.
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
KEYWORD
nonn,hard,more
AUTHOR
EXTENSIONS
More terms from Robert G. Wilson v, Jan 05 2001
a(14)-a(19) from Predrag Kurtovic, May 24 2015
STATUS
approved