Numbers whose base-10 representation has the same number of 2's and 4's.

Terms

a(0) =0a(1) =1a(2) =3a(3) =5a(4) =6a(5) =7a(6) =8a(7) =9a(8) =10a(9) =11a(10) =13a(11) =15a(12) =16a(13) =17a(14) =18a(15) =19a(16) =24a(17) =30a(18) =31a(19) =33a(20) =35a(21) =36a(22) =37a(23) =38a(24) =39a(25) =42a(26) =50a(27) =51a(28) =53a(29) =55