a(n) = 3^n*binomial(2*n+1, n).

Terms

a(0) =1a(1) =9a(2) =90a(3) =945a(4) =10206a(5) =112266a(6) =1250964a(7) =14073345a(8) =159497910a(9) =1818276174a(10) =20827527084a(11) =239516561466