Left-to-right binary enumeration.

Terms

a(0) =1a(1) =2a(2) =11a(3) =21a(4) =12a(5) =22a(6) =111a(7) =211a(8) =121a(9) =221a(10) =112a(11) =212a(12) =122a(13) =222a(14) =1111a(15) =2111a(16) =1211a(17) =2211a(18) =1121a(19) =2121a(20) =1221a(21) =2221a(22) =1112a(23) =2112a(24) =1212a(25) =2212a(26) =1122a(27) =2122a(28) =1222a(29) =2222