Numbers k such that k prefixed by '1' and followed by '9' is a prime.

Terms

a(0) =0a(1) =3a(2) =4a(3) =7a(4) =9a(5) =10a(6) =12a(7) =22a(8) =24a(9) =25a(10) =27a(11) =28a(12) =31a(13) =39a(14) =40a(15) =42a(16) =43a(17) =45a(18) =48a(19) =49a(20) =54a(21) =55a(22) =57a(23) =60a(24) =61a(25) =66a(26) =69a(27) =70a(28) =75a(29) =78