A113551(n)/A006882(n).

Terms

a(0) =1a(1) =4a(2) =35a(3) =240a(4) =3003a(5) =26880a(6) =415701a(7) =4435200a(8) =79676025a(9) =968647680a(10) =19535112675a(11) =263472168960