a(n) = (n+2)! * (n+1)! * n! / 2.A090443a(n) = (n+2)! * (n+1)! * n! / 2.Terms a(0) =1a(1) =6a(2) =144a(3) =8640a(4) =1036800a(5) =217728000a(6) =73156608000External referencesoeis: A090443