%I #12 Nov 29 2023 07:03:45

%S 19,31,79,271,1039,4111,65551,4194319,67108879,1073741839,4294967311,

%T 1099511627791,4398046511119,70368744177679,4722366482869645213711,

%U 75557863725914323419151

%N Primes of the form 4^k + 15.

%C Subsequence of A144487.

%H Vincenzo Librandi, <a href="/A237418/b237418.txt">Table of n, a(n) for n = 1..26</a>

%F a(n) = 4^A253773(n) + 15. - _Elmo R. Oliveira_, Nov 28 2023

%e 65551 is a term because 4^8 + 15 = 65551 is prime.

%t Select[Table[4^n + 15, {n, 1, 200}],PrimeQ]

%o (Magma) [a: n in [1..70] | IsPrime(a) where a is 4^n+15];

%Y Cf. A000040, A144487, A253773 (corresponding k's).

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Feb 22 2014