Digit '7' concatenated with a(n) is a prime.

Terms

a(0) =1a(1) =3a(2) =9a(3) =19a(4) =27a(5) =33a(6) =39a(7) =43a(8) =51a(9) =57a(10) =61a(11) =69a(12) =73a(13) =87a(14) =97a(15) =103a(16) =109a(17) =121a(18) =127a(19) =129a(20) =151a(21) =159a(22) =177a(23) =187a(24) =193a(25) =207a(26) =211a(27) =213a(28) =219a(29) =229