a(n) = n + Sum_{k=0..n} k!.

Terms

a(0) =1a(1) =3a(2) =6a(3) =13a(4) =38a(5) =159a(6) =880a(7) =5921a(8) =46242a(9) =409123a(10) =4037924a(11) =43954725a(12) =522956326a(13) =6749977127a(14) =93928268328