A217381 Numbers k such that 8^k + 7 is prime.

2, 6, 10, 26, 42, 58, 68, 196, 266, 602, 1170, 1288, 1290, 2990, 4110, 6292, 7446, 36928, 57490, 65478, 78570, 188832, 273452

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 A057195.

Naturally these numbers are even because (9-1)^(2n+1)+7 is divisible by 3. - Bruno Berselli, Oct 03 2012

Crossrefs

Cf. A057195, A217354, A217355.

Cf. A144360 (associated primes).

Programs

Mathematica

Select[Range[10000], PrimeQ[8^# + 7] &]

PARI

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

Extensions

a(18)-a(22) from A057195 by Robert Price, Jul 23 2017

a(23) from the data at A057195 added by Amiram Eldar, Jul 23 2025