Primes that contain digits 1 and 9 only.

Terms

a(0) =11a(1) =19a(2) =191a(3) =199a(4) =911a(5) =919a(6) =991a(7) =1999a(8) =9199a(9) =11119a(10) =19919a(11) =19991a(12) =91199a(13) =99119a(14) =99191a(15) =99991a(16) =111119a(17) =111191a(18) =111919a(19) =119191a(20) =191119a(21) =191911a(22) =191999a(23) =199999a(24) =911111a(25) =919111a(26) =991999a(27) =999199a(28) =1111991a(29) =1191119