Duplicate of A007909.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =7a(5) =13a(6) =25a(7) =51a(8) =103a(9) =205a(10) =409a(11) =819a(12) =1639a(13) =3277a(14) =6553a(15) =13107a(16) =26215a(17) =52429a(18) =104857