Numbers whose base-10 representation has the same number of 1's and 2's.

Terms

a(0) =0a(1) =3a(2) =4a(3) =5a(4) =6a(5) =7a(6) =8a(7) =9a(8) =12a(9) =21a(10) =30a(11) =33a(12) =34a(13) =35a(14) =36a(15) =37a(16) =38a(17) =39a(18) =40a(19) =43a(20) =44a(21) =45a(22) =46a(23) =47a(24) =48a(25) =49a(26) =50a(27) =53a(28) =54a(29) =55