Numbers k such that 3*k-4 and 2^k-1 are prime.

Terms

a(0) =2a(1) =3a(2) =5a(3) =7a(4) =17a(5) =19a(6) =31a(7) =61a(8) =89a(9) =107a(10) =521a(11) =1279a(12) =9689a(13) =9941a(14) =21701a(15) =23209a(16) =216091a(17) =13466917a(18) =30402457a(19) =57885161