Numbers k such that (10^k - 19)/9 is prime.

Terms

a(0) =3a(1) =4a(2) =6a(3) =9a(4) =34a(5) =36a(6) =126a(7) =141a(8) =160a(9) =286a(10) =678a(11) =1236a(12) =3757a(13) =4681a(14) =4881a(15) =6360a(16) =6588a(17) =7056a(18) =7752a(19) =41925a(20) =43423a(21) =43503a(22) =47565a(23) =52608a(24) =55084a(25) =76069a(26) =199248