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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 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 March 21 22:41 EDT 2018. Contains 301043 sequences. (Running on oeis4.)