

A057172


Numbers n such that (6^n + 1)/7 is a prime.


13



3, 11, 31, 43, 47, 59, 107, 811, 2819, 4817, 9601, 33581, 38447, 41341, 131891, 196337
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OFFSET

1,1


LINKS

Table of n, a(n) for n=1..16.
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.
Eric Weisstein's World of Mathematics, Repunit
H. Lifchitz, Mersenne and Fermat primes field


MATHEMATICA

lst={}; Do[p=(6^n+1)/7; If[PrimeQ[p], AppendTo[lst, n]], {n, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Sep 29 2008 *)


CROSSREFS

Sequence in context: A018781 A119215 A266970 * A277167 A277049 A261148
Adjacent sequences: A057169 A057170 A057171 * A057173 A057174 A057175


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Sep 15 2000


EXTENSIONS

a(12) was discovered by Kamil Duszenko, Jul 15 2003
a(13) was discovered by Henri Lifchitz, Sep 15 2007
a(14) was discovered by Paul Bourdelais, Oct 01 2007
a(15)=131891, a probable prime, was discovered by Paul Bourdelais, Feb 01 2010
a(16)=196337 is a probable prime discovered by Paul Bourdelais, Feb 19 2010


STATUS

approved



