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

Terms

a(0) =9a(1) =15a(2) =51a(3) =63a(4) =66a(5) =67a(6) =68a(7) =69a(8) =72a(9) =79a(10) =86a(11) =93a(12) =99a(13) =105a(14) =108a(15) =109a(16) =110a(17) =111a(18) =120a(19) =127a(20) =134a(21) =141a(22) =156a(23) =162a(24) =205a(25) =211a(26) =254a(27) =260a(28) =303a(29) =309