Numbers of the form 10^k + 1, 3, 7, or 9 for k>=1.

Terms

a(0) =11a(1) =13a(2) =17a(3) =19a(4) =101a(5) =103a(6) =107a(7) =109a(8) =1001a(9) =1003a(10) =1007a(11) =1009a(12) =10001a(13) =10003a(14) =10007a(15) =10009a(16) =100001a(17) =100003a(18) =100007a(19) =100009a(20) =1000001a(21) =1000003a(22) =1000007a(23) =1000009a(24) =10000001a(25) =10000003a(26) =10000007a(27) =10000009a(28) =100000001a(29) =100000003