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 A126856 Numbers n such that (31^n + 1)/32 is prime. 13
 109, 461, 1061, 50777 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are primes. a(5) > 10^5. - Robert Price, Jul 12 2013 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. H. Lifchitz, Mersenne and Fermat primes field MATHEMATICA Do[ p=Prime[n]; If[ PrimeQ[ (31^p + 1)/32 ], Print[p] ], {n, 1, 1100} ] PROG (PARI) is(n)=isprime((31^n+1)/32) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A000978 = numbers n such that (2^n + 1)/3 is prime. Cf. A007658, A057171, A057172, A057173, A057175, A001562, A057177, A057178, A057179, A057180, A057181, A057182, A057183, A057184, A057185, A057186, A057187, A057188, A057189, A057190, A057191, A071380, A071381, A071382. Cf. A084741, A084742, A065507, A126659. Sequence in context: A270249 A174339 A142640 * A142915 A226473 A142366 Adjacent sequences:  A126853 A126854 A126855 * A126857 A126858 A126859 KEYWORD bref,hard,more,nonn AUTHOR Alexander Adamchuk, Mar 23 2007 EXTENSIONS a(4) from Robert Price, Jul 12 2013 STATUS approved

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Last modified December 5 16:21 EST 2019. Contains 329753 sequences. (Running on oeis4.)