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

Terms

a(0) =1a(1) =3a(2) =6a(3) =16a(4) =48a(5) =153a(6) =511a(7) =1761a(8) =6219a(9) =22383a(10) =81804a(11) =302766a(12) =1132475a(13) =4274166a(14) =16256685a(15) =62249167a(16) =239772510a(17) =928398831a(18) =3611539758a(19) =14107963848a(20) =55318781982a(21) =217652858539a(22) =859027927911