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Numbers k such that 8^k + 5 is prime.
4

%I #42 Oct 31 2024 11:23:35

%S 1,47,91,64655

%N Numbers k such that 8^k + 5 is prime.

%C All terms are 1/3 of the terms of A059242 that are multiples of 3.

%C No more terms <= 10^5. - _Tyler NeSmith_

%t Select[Range[1000], PrimeQ[8^# + 5] &]

%o (Magma) [n: n in [0..1000] | IsPrime(8^n + 5)];

%o (PARI) is(n)=ispseudoprime(8^n+5) \\ _Charles R Greathouse IV_, Feb 20 2017

%Y Cf. A059242, A217354.

%K nonn,hard,more

%O 1,2

%A _Vincenzo Librandi_, Oct 02 2012

%E a(4) from _Tyler NeSmith_, Jan 19 2021