A057191 Numbers n such that (25^n+1)/26 is a prime.

3, 7, 23, 29, 59, 1249, 1709, 1823, 1931, 3433, 8863, 43201, 78707

Offset: 1

Author

N. J. A. Sloane, Sep 15 2000

Keywords

• nonn
• more

Comments

Some of the larger terms may only correspond to probable primes.

a(14) > 10^5. - Robert Price, Jun 10 2013

Links

• H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.

Programs

Mathematica

Select[Range[0, 2000], PrimeQ[(25^# + 1) / 26] &] (* Vincenzo Librandi, Oct 29 2017 *)

PARI

isok(n) = (denominator(p=(25^n+1)/26)==1) && isprime(p); \\ Michel Marcus, Oct 29 2017

Extensions

a(12)-a(13) from Robert Price, Jun 10 2013