a(n) = (n! - 6)/6.

Terms

a(0) =0a(1) =3a(2) =19a(3) =119a(4) =839a(5) =6719a(6) =60479a(7) =604799a(8) =6652799a(9) =79833599a(10) =1037836799a(11) =14529715199a(12) =217945727999