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

Terms

a(0) =0a(1) =2a(2) =10a(3) =58a(4) =442a(5) =4282a(6) =50362a(7) =695482a(8) =11017402a(9) =196811962a(10) =3912703162a(11) =85662309562