A071380 Numbers n such that (26^n+1)/27 is a prime.

11, 109, 227, 277, 347, 857, 2297, 9043, 501409

Offset: 1

Author

Rick L. Shepherd, May 22 2002

Keywords

• nonn
• hard
• more

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.

Crossrefs

Cf. A057191, A071381.

Programs

Mathematica

Select[Range[3000], PrimeQ[(26^# + 1) / 27] &] (* Vincenzo Librandi, Oct 29 2017 *)

PARI

isok(n) = (denominator(p=(26^n+1)/27)==1) && isprime(p); \\ Michel Marcus, Oct 29 2017

Extensions

a(9) from Paul Bourdelais, Oct 02 2023