G.f. satisfies A(x) = 1 + x*(1 + x*A(x)^3)^4.

Terms

a(0) =1a(1) =1a(2) =4a(3) =18a(4) =100a(5) =587a(6) =3660a(7) =23640a(8) =157076a(9) =1066281a(10) =7363620a(11) =51568732a(12) =365369868a(13) =2614235293a(14) =18862816112a(15) =137096744232