1,1

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

H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.

J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.

J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.

S. S. Wagstaff, Jr., The Cunningham Project

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.

H. Lifchitz, Mersenne and Fermat primes field

lst={}; Do[If[PrimeQ[(5^n-1)/4], AppendTo[lst, n]], {n, 10^4}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Aug 20 2008]

Sequence in context: A053728 A059055 A145670 this_sequence A000572 A059568 A003512

Adjacent sequences: A004058 A004059 A004060 this_sequence A004062 A004063 A004064

hard,nonn

N. J. A. Sloane (njas(AT)research.att.com).

3 more terms from Kamil Duszenko (kdusz(AT)wp.pl), Mar 25 2003

a(16)=201359 is a probable prime based on trial factoring to 4e13 and Fermat primality testing base 2. Paul Bourdelais (paul.bourdelais(AT)gd-ais.com), Dec 11 2008