Bisection of A000016 (also of A000013).

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =30a(5) =94a(6) =316a(7) =1096a(8) =3856a(9) =13798a(10) =49940a(11) =182362a(12) =671092a(13) =2485534a(14) =9256396a(15) =34636834a(16) =130150588a(17) =490853416a(18) =1857283156a(19) =7048151672a(20) =26817356776a(21) =102280151422a(22) =390937468408