a(n) = (n+2)! * Sum_{k=1..n} 1/k.

Terms

a(0) =0a(1) =6a(2) =36a(3) =220a(4) =1500a(5) =11508a(6) =98784a(7) =940896a(8) =9862560a(9) =112923360a(10) =1402980480a(11) =18804839040a(12) =270532604160