a(n) = n! * Sum_{k=0..n-1} (-2)^k / k!.

Terms

a(0) =0a(1) =1a(2) =-2a(3) =6a(4) =-8a(5) =40a(6) =48a(7) =784a(8) =5248a(9) =49536a(10) =490240a(11) =5403904a(12) =64822272a(13) =842742784a(14) =11798284288a(15) =176974510080