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

Terms

a(0) =1a(1) =1a(2) =3a(3) =12a(4) =57a(5) =285a(6) =1500a(7) =8193a(8) =46011a(9) =263991a(10) =1540783a(11) =9119145a(12) =54601746a(13) =330153384a(14) =2013112923a(15) =12364421871a(16) =76425011259a(17) =475036074345