A257790 Numbers k such that 6*5^k - 1 is prime.

0, 1, 2, 5, 11, 28, 65, 72, 361, 479, 494, 599, 1062, 1094, 1193, 2827, 3271, 3388, 3990, 4418, 11178, 16294, 25176, 42500, 68320, 85698, 145259, 159119, 169771, 252665, 412051

Offset: 1

Author

Robert Price, May 08 2015

Keywords

• nonn
• hard
• more

Comments

All terms correspond to verified primes, that is, not merely probable primes.

Crossrefs

Cf. A143279.

Programs

Magma

[n: n in [0..2*10^3] | IsPrime(6*5^n-1)]; // Vincenzo Librandi, May 09 2015

Mathematica

Select[Range[0, 10000], PrimeQ[6*5^# - 1] &]

PARI

is(n)=ispseudoprime(6*5^n-1) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(30) from Riley Fisher, Sep 20 2024

a(31) from Riley Fisher, Dec 09 2024