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A057172
Numbers n such that (6^n + 1)/7 is a prime.
14
3, 11, 31, 43, 47, 59, 107, 811, 2819, 4817, 9601, 33581, 38447, 41341, 131891, 196337, 1313371
OFFSET
1,1
COMMENTS
a(15), a(16) and a(17) correspond to probable primes.
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.
Eric Weisstein's World of Mathematics, Repunit
MATHEMATICA
Select[Range[5000], PrimeQ[(6^# + 1) / 7] &] (* Vincenzo Librandi, Oct 29 2017 *)
PROG
(PARI) isok(n) = (denominator(p=(6^n+1)/7)==1) && isprime(p); \\ Michel Marcus, Oct 29 2017
CROSSREFS
Sequence in context: A018781 A119215 A266970 * A277167 A277049 A261148
KEYWORD
nonn,more
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) was discovered by Paul Bourdelais, Feb 01 2010
a(16) was discovered by Paul Bourdelais, Feb 19 2010
a(17) was discovered by Paul Bourdelais, Jan 28 2019
STATUS
approved