a(n) = n! - 2.

Terms

a(0) =-1a(1) =-1a(2) =0a(3) =4a(4) =22a(5) =118a(6) =718a(7) =5038a(8) =40318a(9) =362878a(10) =3628798a(11) =39916798a(12) =479001598a(13) =6227020798a(14) =87178291198