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

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =20a(5) =85a(6) =534a(7) =3703a(8) =29672a(9) =266985a(10) =2669930a(11) =29369131a(12) =352429692a(13) =4581585853a(14) =64142202110a(15) =962133031455