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

Terms

a(0) =2a(1) =3a(2) =20a(3) =70a(4) =564a(5) =3108a(6) =30624a(7) =230256a(8) =2705760a(9) =25771680a(10) =352805760a(11) =4067556480a(12) =63651813120a(13) =861371884800