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Numbers k such that 8^k - 7 is prime.
1

%I #22 Sep 15 2024 14:31:54

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

%N Numbers k such that 8^k - 7 is prime.

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

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

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

%o (PARI) is(n)=ispseudoprime(8^n-7) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A059609, A217353, A217356.

%K nonn,more

%O 1,1

%A _Vincenzo Librandi_, Oct 02 2012

%E a(7) using A059609 from _Michael S. Branicky_, Sep 15 2024