Concatenate n and n-1 in binary.

Terms

a(0) =10a(1) =101a(2) =1110a(3) =10011a(4) =101100a(5) =110101a(6) =111110a(7) =1000111a(8) =10011000a(9) =10101001a(10) =10111010a(11) =11001011a(12) =11011100a(13) =11101101a(14) =11111110a(15) =100001111a(16) =1000110000a(17) =1001010001a(18) =1001110010a(19) =1010010011a(20) =1010110100a(21) =1011010101a(22) =1011110110a(23) =1100010111a(24) =1100111000a(25) =1101011001a(26) =1101111010a(27) =1110011011a(28) =1110111100