a(n) = 1 + Sum_{k=0..n} 2^k*k!.

Terms

a(0) =1a(1) =2a(2) =4a(3) =12a(4) =60a(5) =444a(6) =4284a(7) =50364a(8) =695484a(9) =11017404a(10) =196811964a(11) =3912703164a(12) =85662309564