OFFSET
1,1
COMMENTS
All terms are primes.
a(5) > 10^5.
LINKS
J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.
H. Lifchitz, Mersenne and Fermat primes field
Eric Weisstein's World of Mathematics, Repunit.
MATHEMATICA
Do[ p=Prime[n]; If[ PrimeQ[ (39^p + 1)/40 ], Print[p] ], {n, 1, 9592} ]
PROG
(PARI) is(n)=ispseudoprime((39^n+1)/40) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
Cf. A000978 (numbers n such that (2^n + 1)/3 is prime).
KEYWORD
hard,more,nonn
AUTHOR
Robert Price, Oct 05 2013
STATUS
approved