a(1) = 1; a(n+1) = Sum_{d|n} 2^(n/d - 1) * a(d).

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =17a(5) =33a(6) =75a(7) =139a(8) =289a(9) =557a(10) =1119a(11) =2143a(12) =4341a(13) =8437a(14) =16843a(15) =33343a(16) =66573a(17) =132109a(18) =264243a(19) =526387a(20) =1052549a(21) =2101617a(22) =4202031a(23) =8396335a(24) =16792705a(25) =33570193a(26) =67137403a(27) =134248191a(28) =268492033a(29) =536927489