Sequence A115809 in binary.

Terms

a(0) =0a(1) =11111a(2) =111110a(3) =111111a(4) =1111100a(5) =1111110a(6) =1111111a(7) =11111000a(8) =11111100a(9) =11111110a(10) =11111111a(11) =111110000a(12) =111111000a(13) =111111100a(14) =111111110a(15) =111111111a(16) =1111100000a(17) =1111110000a(18) =1111111000a(19) =1111111100a(20) =1111111110a(21) =1111111111