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

Terms

a(0) =1a(1) =6a(2) =40a(3) =280a(4) =2016a(5) =14784a(6) =109824a(7) =823680a(8) =6223360a(9) =47297536a(10) =361181184a(11) =2769055744a(12) =21300428800a(13) =164317593600