a(n) = (-1)^n * n!.

Terms

a(0) =1a(1) =-1a(2) =2a(3) =-6a(4) =24a(5) =-120a(6) =720a(7) =-5040a(8) =40320a(9) =-362880a(10) =3628800a(11) =-39916800a(12) =479001600a(13) =-6227020800a(14) =87178291200