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URL: https://oeis.org/A071380

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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
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
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
Sequence in context: A156935 A308965 A377350 * A142423 A159495 A125423
KEYWORD
nonn,hard,more
AUTHOR
Rick L. Shepherd, May 22 2002
EXTENSIONS
a(9) from Paul Bourdelais, Oct 02 2023
STATUS
approved