Exactly 2 digits from {1,2,3,4,5,6,7,8,9} can precede a(n) to form a prime.

Terms

a(0) =17a(1) =117a(2) =119a(3) =123a(4) =131a(5) =143a(6) =147a(7) =157a(8) =159a(9) =173a(10) =177a(11) =191a(12) =193a(13) =197a(14) =199a(15) =201a(16) =207a(17) =227a(18) =233a(19) =239a(20) =241a(21) =247a(22) =251a(23) =261a(24) =263a(25) =279a(26) =289a(27) =291a(28) =299a(29) =303