G.f.: (1-4*x)^(-1/2) * (1-8*x)^(-1/4).

Terms

a(0) =1a(1) =4a(2) =20a(3) =112a(4) =680a(5) =4384a(6) =29536a(7) =205440a(8) =1462368a(9) =10587520a(10) =77633920a(11) =574845440a(12) =4289409280a(13) =32206976000a(14) =243074083840