n!*(3*n^2-13*n+14)/6.

Terms

a(0) =0a(1) =2a(2) =40a(3) =480a(4) =5280a(5) =58800a(6) =685440a(7) =8467200a(8) =111283200a(9) =1556755200a(10) =23151744000a(11) =365318553600