Numbers whose decimal expansion contains only 0's and 4's.

Terms

a(0) =0a(1) =4a(2) =40a(3) =44a(4) =400a(5) =404a(6) =440a(7) =444a(8) =4000a(9) =4004a(10) =4040a(11) =4044a(12) =4400a(13) =4404a(14) =4440a(15) =4444a(16) =40000a(17) =40004a(18) =40040a(19) =40044a(20) =40400a(21) =40404a(22) =40440a(23) =40444a(24) =44000a(25) =44004a(26) =44040a(27) =44044a(28) =44400a(29) =44404