Bisection of A000011.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =23a(5) =63a(6) =190a(7) =612a(8) =2056a(9) =7155a(10) =25482a(11) =92205a(12) =337594a(13) =1246863a(14) =4636390a(15) =17334801a(16) =65108062a(17) =245492244a(18) =928772650a(19) =3524337980a(20) =13409202676a(21) =51141124287a(22) =195470831356a(23) =748607855769