a(n) = n^n*binomial(n+2, 2).

Terms

a(0) =1a(1) =3a(2) =24a(3) =270a(4) =3840a(5) =65625a(6) =1306368a(7) =29647548a(8) =754974720a(9) =21308126895a(10) =660000000000