Becomes a prime if a 1 is inserted before each digit.

Terms

a(0) =1a(1) =3a(2) =7a(3) =9a(4) =17a(5) =23a(6) =27a(7) =39a(8) =51a(9) =63a(10) =69a(11) =81a(12) =93a(13) =119a(14) =121a(15) =127a(16) =137a(17) =161a(18) =193a(19) =199a(20) =203a(21) =209a(22) =233a(23) =271a(24) =301a(25) =311a(26) =313a(27) =323a(28) =331a(29) =337