Write n in binary, delete 0's.

Terms

a(0) =1a(1) =1a(2) =11a(3) =1a(4) =11a(5) =11a(6) =111a(7) =1a(8) =11a(9) =11a(10) =111a(11) =11a(12) =111a(13) =111a(14) =1111a(15) =1a(16) =11a(17) =11a(18) =111a(19) =11a(20) =111a(21) =111a(22) =1111a(23) =11a(24) =111a(25) =111a(26) =1111a(27) =111a(28) =1111a(29) =1111