G.f. satisfies A(x) = Product_{n>=1} (1 + x^n*A(x)^2).

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =43a(5) =179a(6) =778a(7) =3491a(8) =16051a(9) =75235a(10) =358170a(11) =1727124a(12) =8418266a(13) =41408344a(14) =205289265a(15) =1024737905a(16) =5145933602a(17) =25978844478a(18) =131773584768a(19) =671239285119