Duplicate of A068425.

Terms

a(0) =3a(1) =6a(2) =12a(3) =25a(4) =50a(5) =100a(6) =201a(7) =402a(8) =804a(9) =1608a(10) =3216a(11) =6433a(12) =12867a(13) =25735a(14) =51471a(15) =102943a(16) =205887