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

Terms

a(0) =0a(1) =2a(2) =5a(3) =20a(4) =111a(5) =704a(6) =5015a(7) =40284a(8) =362831a(9) =3628736a(10) =39916719a(11) =479001500a(12) =6227020679a(13) =87178291056