A128338 - OEIS

%I #10 Nov 01 2018 21:25:43

%S 7,19,167,173,223,281,21647

%N Numbers k such that (8^k + 5^k)/13 is prime.

%C All terms are primes.

%C a(8) > 10^5. - _Robert Price_, Jan 21 2013

%t k=8; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n,1,100}]

%o (PARI) is(n)=isprime((8^n+5^n)/13) \\ _Charles R Greathouse IV_, Feb 17 2017

%Y Cf. A057171, A082387, A122853, A128335, A128336, A128337, A128339, A128340, A128341, A128342, A128343. Cf. A004061, A082182, A121877, A059802. Cf. A062572, A128344, A128345, A128346, A128347, A128348, A128349, A128350, A128351, A128352, A128353, A128354.

%K hard,more,nonn

%O 1,1

%A _Alexander Adamchuk_, Feb 27 2007

%E a(7) from _Robert Price_, Jan 21 2013