a(n) = round(Gamma(n+2/3)/Gamma(2/3)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =11a(5) =51a(6) =287a(7) =1915a(8) =14684a(9) =127262a(10) =1230202a(11) =13122150a(12) =153091745a(13) =1939162101a(14) =26501882045a(15) =388694270000