Bisection of Motzkin sums (A005043).

Terms

a(0) =1a(1) =1a(2) =3a(3) =15a(4) =91a(5) =603a(6) =4213a(7) =30537a(8) =227475a(9) =1730787a(10) =13393689a(11) =105089229a(12) =834086421a(13) =6684761125a(14) =54022715451a(15) =439742222071