A128339 - OEIS

%I #21 Sep 08 2022 08:45:30

%S 3,5,13,17,43,127,229,277,6043,11131,11821

%N Numbers k such that (9^k + 5^k)/14 is prime.

%C All terms are primes.

%C a(12) > 10^5. - _Robert Price_, Dec 26 2012

%t k=9; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n,1,100}]

%o (PARI) is(n)=isprime((9^n+5^n)/14) \\ _Charles R Greathouse IV_, Feb 17 2017

%o (Magma) [n: n in [3..300] |IsPrime((9^n + 5^n) div 14)]; // _Vincenzo Librandi_, Nov 02 2018

%Y Cf. A057171, A082387, A122853, A128335, A128336, A128337, A128338, 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 3 more PRP terms from _Sean A. Irvine_, Oct 01 2009