Duplicate of A002548.

Terms

a(0) =1a(1) =1a(2) =12a(3) =6a(4) =180a(5) =10a(6) =560a(7) =1260a(8) =12600a(9) =1260a(10) =166320a(11) =13860a(12) =2522520a(13) =2702700