A217352 Numbers k such that 6^k - 7 is prime.

2, 4, 6, 8, 9, 10, 15, 20, 46, 49, 61, 98, 110, 144, 266, 344, 978, 1692, 1880, 1924, 3142, 3220, 4209, 5708, 7064, 13465, 13858, 19474, 22666, 26807

Offset: 1

Author

Vincenzo Librandi, Oct 02 2012

Keywords

• nonn
• more
• hard

Comments

a(31) > 50000. - Michael S. Branicky, Oct 27 2024

Crossrefs

Cf. A059614, A217351.

Programs

Mathematica

Select[Range[10000], PrimeQ[6^# - 7] &]

PARI

is(n)=ispseudoprime(6^n-7) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(26)-a(27) from Michael S. Branicky, Jan 29 2023

a(28)-a(29) from Michael S. Branicky, Apr 10 2023

a(30) from Michael S. Branicky, Oct 27 2024