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

Terms

a(0) =1a(1) =2a(2) =9a(3) =48a(4) =25a(5) =2160a(6) =2205a(7) =17920a(8) =5103a(9) =18144000a(10) =21175a(11) =2874009600a(12) =11293425a(13) =100452352a(14) =9577693125a(16) =253127875a(18) =282135852999