Write 0, 1, ..., n in binary and add as if they were decimal numbers.

Terms

a(0) =0a(1) =1a(2) =11a(3) =22a(4) =122a(5) =223a(6) =333a(7) =444a(8) =1444a(9) =2445a(10) =3455a(11) =4466a(12) =5566a(13) =6667a(14) =7777a(15) =8888a(16) =18888a(17) =28889a(18) =38899a(19) =48910a(20) =59010a(21) =69111a(22) =79221a(23) =89332a(24) =100332a(25) =111333a(26) =122343a(27) =133354a(28) =144454a(29) =155555