G.f. satisfies A(x) = 1 + x*A(x)^2*(1 + x^3*A(x)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =15a(5) =47a(6) =153a(7) =513a(8) =1763a(9) =6177a(10) =21981a(11) =79224a(12) =288611a(13) =1061019a(14) =3931320a(15) =14666135a(16) =55041855a(17) =207668702a(18) =787225265a(19) =2996851140a(20) =11452198368a(21) =43915195973a(22) =168930713580a(23) =651708006690