(1/n)*A073617(n+1).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =6a(5) =40a(6) =150a(7) =2100a(8) =14700a(9) =423360a(10) =5556600a(11) =325987200a(12) =8068183200a(13) =958961203200