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

Terms

a(0) =1a(1) =2a(2) =12a(3) =80a(4) =560a(5) =4032a(6) =29568a(7) =219648a(8) =1647360a(9) =12446720a(10) =94595072a(11) =722362368a(12) =5538111488a(13) =42600857600a(14) =328635187200