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A057181 Numbers n such that (15^n + 1)/16 is a prime. 15
3, 7, 29, 1091, 2423, 54449, 67489, 551927 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(6), a(7) and a(8) correspond to probable primes.

LINKS

Table of n, a(n) for n=1..8.

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 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

MATHEMATICA

Select[Range[3000], PrimeQ[(15^# + 1) / 16] &] (* Vincenzo Librandi, Oct 29 2017 *)

PROG

(Prime95) PRP=1, 15, 551927, 1, 0, 0, "16"

(PARI) isok(n) = (denominator(p=(15^n+1)/16)==1) && isprime(p); \\ Michel Marcus, Oct 29 2017

CROSSREFS

Sequence in context: A048722 A061955 A113834 * A227077 A136934 A201794

Adjacent sequences:  A057178 A057179 A057180 * A057182 A057183 A057184

KEYWORD

nonn,more

AUTHOR

N. J. A. Sloane, Sep 15 2000

EXTENSIONS

a(6) from Paul Bourdelais, Mar 15 2010

a(7) from Paul Bourdelais, Mar 16 2010

a(8) from Paul Bourdelais, Jul 03 2013

STATUS

approved

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Last modified June 19 04:44 EDT 2019. Contains 324217 sequences. (Running on oeis4.)