Numbers whose base-7 representation has the same number of 1's and 2's.

Terms

a(0) =0a(1) =3a(2) =4a(3) =5a(4) =6a(5) =9a(6) =15a(7) =21a(8) =24a(9) =25a(10) =26a(11) =27a(12) =28a(13) =31a(14) =32a(15) =33a(16) =34a(17) =35a(18) =38a(19) =39a(20) =40a(21) =41a(22) =42a(23) =45a(24) =46a(25) =47a(26) =48a(27) =51a(28) =63a(29) =66