Numbers whose base-7 representation has the same number of 0's and 3's.

Terms

a(0) =1a(1) =2a(2) =4a(3) =5a(4) =6a(5) =8a(6) =9a(7) =11a(8) =12a(9) =13a(10) =15a(11) =16a(12) =18a(13) =19a(14) =20a(15) =21a(16) =29a(17) =30a(18) =32a(19) =33a(20) =34a(21) =36a(22) =37a(23) =39a(24) =40a(25) =41a(26) =43a(27) =44a(28) =46a(29) =47