a(n) = 2^n*(3*n)!/(n!*(2*n)!).

Terms

a(0) =1a(1) =6a(2) =60a(3) =672a(4) =7920a(5) =96096a(6) =1188096a(7) =14883840a(8) =188280576a(9) =2399654400a(10) =30766095360a(11) =396363202560