a(n) = Sum_{k=1..n} k!.

Terms

a(0) =0a(1) =1a(2) =3a(3) =9a(4) =33a(5) =153a(6) =873a(7) =5913a(8) =46233a(9) =409113a(10) =4037913a(11) =43954713a(12) =522956313a(13) =6749977113a(14) =93928268313