%I

%S 7,53,67,71,443,26497

%N Numbers n such that (11^n + 4^n)/15 is prime.

%C All terms are prime.

%C a(7) > 10^5.

%t Select[ Prime[ Range[1, 100000] ], PrimeQ[ (11^# + 4^#)/15 ]& ]

%o (PARI) is(n)=ispseudoprime((11^n+4^n)/15) \\ _Charles R Greathouse IV_, Jun 06 2017

%Y Cf. A057178, A128341, A181141, A187819, A217095.

%K hard,nonn,more

%O 1,1

%A _Robert Price_, Apr 08 2013