Numbers with digits 4 and 9 only.

Terms

a(0) =4a(1) =9a(2) =44a(3) =49a(4) =94a(5) =99a(6) =444a(7) =449a(8) =494a(9) =499a(10) =944a(11) =949a(12) =994a(13) =999a(14) =4444a(15) =4449a(16) =4494a(17) =4499a(18) =4944a(19) =4949a(20) =4994a(21) =4999a(22) =9444a(23) =9449a(24) =9494a(25) =9499a(26) =9944a(27) =9949a(28) =9994a(29) =9999