Numbers whose base-7 representation has the same number of 1's and 3's.

Terms

a(0) =0a(1) =2a(2) =4a(3) =5a(4) =6a(5) =10a(6) =14a(7) =16a(8) =18a(9) =19a(10) =20a(11) =22a(12) =28a(13) =30a(14) =32a(15) =33a(16) =34a(17) =35a(18) =37a(19) =39a(20) =40a(21) =41a(22) =42a(23) =44a(24) =46a(25) =47a(26) =48a(27) =52a(28) =66a(29) =70