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

Terms

a(0) =-2a(1) =1a(2) =-7a(3) =23a(4) =-121a(5) =719a(6) =-5041a(7) =40319a(8) =-362881a(9) =3628799a(10) =-39916801a(11) =479001599a(12) =-6227020801a(13) =87178291199