a(n) = (n-1)!-n^tau(n)/n^2.

Terms

a(0) =0a(1) =1a(2) =2a(3) =23a(4) =84a(5) =719a(6) =4976a(7) =40311a(8) =362780a(9) =3628799a(10) =39896064a(11) =479001599a(12) =6227020604a(13) =87178290975