a(n) is the number whose binary representation is A138144(n).

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =27a(5) =51a(6) =99a(7) =195a(8) =387a(9) =771a(10) =1539a(11) =3075a(12) =6147a(13) =12291a(14) =24579a(15) =49155a(16) =98307a(17) =196611a(18) =393219a(19) =786435a(20) =1572867a(21) =3145731a(22) =6291459a(23) =12582915a(24) =25165827a(25) =50331651a(26) =100663299a(27) =201326595a(28) =402653187a(29) =805306371