a(n) = n!*(n-1)!/2^(n-1).

A006472

a(n) = n!*(n-1)!/2^(n-1).

Terms

    a(0) =1a(1) =1a(2) =3a(3) =18a(4) =180a(5) =2700a(6) =56700a(7) =1587600a(8) =57153600a(9) =2571912000a(10) =141455160000

External references