

A004063


Numbers n such that (7^n  1)/6 is prime.
(Formerly M3836)


18




OFFSET

1,1


COMMENTS

Base 7 repunit primes.  Paul Bourdelais, Aug 31 2007
For Repunits with bases from 11 to 11, base 7 Repunits have the lowest relative rate of occurrence so far.  Paul Bourdelais, Feb 23 2010


REFERENCES

J. Brillhart et al., Factorizations of b^n + 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Table of n, a(n) for n=1..10.
Paul Bourdelais,A Generalized Repunit Conjecture
J. Brillhart et al., Factorizations of b^n + 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927930.
H. Lifchitz, Mersenne and Fermat primes field
S. S. Wagstaff, Jr., The Cunningham Project
Eric Weisstein's World of Mathematics, Repunit.


MATHEMATICA

For[n = 1, n <= 20000, n++, If[PrimeQ[(7^n  1)/6 ], Print[n]]] (* Sam Handler (sam_5_5_5_0(AT)yahoo.com), Aug 09 2006 *)


PROG

(Prime95) PRP=1, 7, 1264699, 1, 0, 0, "6"
(PARI) is(n)=isprime((7^n  1)/6) \\ Charles R Greathouse IV, Apr 28 2015


CROSSREFS

Sequence in context: A228280 A155175 A213129 * A005764 A099974 A247820
Adjacent sequences: A004060 A004061 A004062 * A004064 A004065 A004066


KEYWORD

nonn,hard


AUTHOR

N. J. A. Sloane.


EXTENSIONS

a(6) from Robert G. Wilson v, Apr 09 2005
a(7)=35201 is a probable prime from Paul Bourdelais, Aug 31 2007
a(8)=126037 discovered Sep 17 2008 by Paul Bourdelais & Eric Purohit  it is a probable prime based on trial factoring to 2.5*10^13 and Fermat base 2 primality test.  Paul Bourdelais, Sep 18 2008
a(9)=371669 is a probable prime discovered by Paul Bourdelais, Feb 23 2010
a(10)=1264699 is a probable prime discovered by Paul Bourdelais, Jan 06 2014


STATUS

approved



