a(n) = n! - 1.

Terms

a(0) =0a(1) =0a(2) =1a(3) =5a(4) =23a(5) =119a(6) =719a(7) =5039a(8) =40319a(9) =362879a(10) =3628799a(11) =39916799a(12) =479001599a(13) =6227020799a(14) =87178291199