Numbers using only digits 1 and 9.

Terms

a(0) =1a(1) =9a(2) =11a(3) =19a(4) =91a(5) =99a(6) =111a(7) =119a(8) =191a(9) =199a(10) =911a(11) =919a(12) =991a(13) =999a(14) =1111a(15) =1119a(16) =1191a(17) =1199a(18) =1911a(19) =1919a(20) =1991a(21) =1999a(22) =9111a(23) =9119a(24) =9191a(25) =9199a(26) =9911a(27) =9919a(28) =9991a(29) =9999