Numbers k such that (6^k - 1)/5 is prime.

Terms

a(0) =2a(1) =3a(2) =7a(3) =29a(4) =71a(5) =127a(6) =271a(7) =509a(8) =1049a(9) =6389a(10) =6883a(11) =10613a(12) =19889a(13) =79987a(14) =608099a(15) =1365019a(16) =3360347