A217380 Numbers k such that 8^k - 7 is prime.

13, 661, 773, 833, 4273, 40613, 302913

Offset: 1

Author

Vincenzo Librandi, Oct 02 2012

Keywords

• nonn
• more

Comments

All terms are equal to 1/3 of the multiples of 3 in A059609.

Naturally these numbers are odd since (9-1)^(2n)-7 is divisible by 3. - Bruno Berselli, Oct 04 2012

Crossrefs

Cf. A059609, A217353, A217356.

Programs

Mathematica

Select[Range[4000], PrimeQ[8^# - 7] &]

PARI

is(n)=ispseudoprime(8^n-7) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(7) using A059609 from Michael S. Branicky, Sep 15 2024