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

Terms

a(0) =1a(1) =3a(2) =6a(3) =11a(4) =24a(5) =66a(6) =196a(7) =576a(8) =1692a(9) =5110a(10) =15933a(11) =50604a(12) =161988a(13) =521700a(14) =1693362a(15) =5541679a(16) =18260055a(17) =60487659a(18) =201272437a(19) =672550158a(20) =2256204327a(21) =7596059333a(22) =25655943417a(23) =86904524289a(24) =295154911774