a(n) = 3*binomial(6*n+9,n)/(2*n+3).

Terms

a(0) =1a(1) =9a(2) =90a(3) =975a(4) =11160a(5) =132867a(6) =1629012a(7) =20430900a(8) =260907075a(9) =3381098545a(10) =44352058608a(11) =587787511779