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 A229663 Numbers n such that (40^n + 1)/41 is prime. 6
 53, 67, 1217, 5867, 6143, 11681, 29959 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are primes. a(8) > 10^5. 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. H. Lifchitz, Mersenne and Fermat primes field Eric Weisstein's World of Mathematics, Repunit. MATHEMATICA Do[ p=Prime[n]; If[ PrimeQ[ (40^p + 1)/41 ], Print[p] ], {n, 1, 9592} ] PROG (PARI) is(n)=ispseudoprime((40^n+1)/41) \\ 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, A084741, A084742, A065507, A126659, A126856, A185240, A229145, A229524. Sequence in context: A182571 A034965 A160029 * A223091 A301479 A244187 Adjacent sequences:  A229660 A229661 A229662 * A229664 A229665 A229666 KEYWORD hard,more,nonn AUTHOR Robert Price, Sep 27 2013 STATUS approved

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Last modified December 10 12:22 EST 2019. Contains 329895 sequences. (Running on oeis4.)