The Roman numerals, with "i" replaced by "1", "v" replaced by "5", "x" replaced by 10, etc.

Terms

a(0) =1a(1) =11a(2) =111a(3) =15a(4) =5a(5) =51a(6) =511a(7) =5111a(8) =110a(9) =10a(10) =101a(11) =1011a(12) =10111a(13) =1015a(14) =105a(15) =1051a(16) =10511a(17) =105111a(18) =10110a(19) =1010a(20) =10101a(21) =101011a(22) =1010111a(23) =101015a(24) =10105a(25) =101051a(26) =1010511a(27) =10105111a(28) =1010110a(29) =101010