a(n) = Sum_{i=0..n} 2^i*i!.

Terms

a(0) =1a(1) =3a(2) =11a(3) =59a(4) =443a(5) =4283a(6) =50363a(7) =695483a(8) =11017403a(9) =196811963a(10) =3912703163a(11) =85662309563