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

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =24a(5) =139a(6) =853a(7) =5886a(8) =46198a(9) =409069a(10) =4037859a(11) =43954648a(12) =522956236a(13) =6749977023a(14) =93928268209