a(n) = (2^n - 1)*n!.

Terms

a(0) =0a(1) =1a(2) =6a(3) =42a(4) =360a(5) =3720a(6) =45360a(7) =640080a(8) =10281600a(9) =185431680a(10) =3712262400a(11) =81709689600