%I #12 Nov 14 2019 19:57:02

%S 1,2,6,9,20,46,58,64,69,110,158,178,186,268,424,624,641,1236,1593,

%T 2264,2870,5797,7518,7688,9300

%N Numbers n such that r3(k) * 2^n + 1 is prime, where r3() = A002277 and k is the number of decimal digits of 2^n.

%C a(1) through a(25) have been proved to be prime with WinPFGW. a(25) has 5600 digits. No more terms up to 12800.

%C Results were computed using the PrimeFormGW (PFGW) primality-testing program. - _Hugo Pfoertner_, Nov 14 2019

%e a(4)=9 because 333 * 2^9 + 1 = 170497, a prime.

%K more,nonn,base

%O 1,2

%A _Jason Earls_, Jul 15 2004