a(n) = n! - 2*n.

Terms

a(0) =1a(1) =-1a(2) =-2a(3) =0a(4) =16a(5) =110a(6) =708a(7) =5026a(8) =40304a(9) =362862a(10) =3628780a(11) =39916778a(12) =479001576a(13) =6227020774a(14) =87178291172