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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =8a(5) =64a(6) =504a(7) =4132a(8) =36224a(9) =343197a(10) =3528800a(11) =39382654a(12) =476015616a(13) =6209617492a(14) =87072877696