%I #17 Jul 15 2023 08:34:33
%S 1,7,9,33,127,153,2327,3607,14803,16431
%N Numbers k such that 11^k + 3^k - 1 is prime.
%C a(9) > 13518. - _Daniel Starodubtsev_, Apr 06 2020
%F A177027(n) = 11^a(n)+3^a(n)-1.
%e 7 is in the sequence, because 11^7 + 3^7 - 1 = 19489357 is prime.
%o (Magma)[n: n in [0..1500]|IsPrime(11^n+3^n-1^n)]
%o (PARI) is(n)=ispseudoprime(11^n+3^n-1) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A155623, A177027.
%K nonn,more
%O 1,2
%A _Vincenzo Librandi_, Dec 09 2010
%E a(7)-a(8) from _Daniel Starodubtsev_, Apr 06 2020
%E a(9)-a(10) from _Michael S. Branicky_, Jul 15 2023