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 A071380 Numbers n such that (26^n+1)/27 is a prime. 15
 11, 109, 227, 277, 347, 857, 2297, 9043, 501409 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Some of the larger terms may only correspond to probable primes. a(9) > 10^5. - Robert Price, Jul 07 2013 LINKS Table of n, a(n) for n=1..9. H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7. MATHEMATICA Select[Range[3000], PrimeQ[(26^# + 1) / 27] &] (* Vincenzo Librandi, Oct 29 2017 *) PROG (PARI) isok(n) = (denominator(p=(26^n+1)/27)==1) && isprime(p); \\ Michel Marcus, Oct 29 2017 CROSSREFS Cf. A057191, A071381. Sequence in context: A080158 A156935 A308965 * A142423 A159495 A125423 Adjacent sequences: A071377 A071378 A071379 * A071381 A071382 A071383 KEYWORD nonn,hard,more AUTHOR Rick L. Shepherd, May 22 2002 EXTENSIONS a(9) from Paul Bourdelais, Oct 02 2023 STATUS approved

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Last modified August 14 00:08 EDT 2024. Contains 375146 sequences. (Running on oeis4.)