a(n) = 2*n^(n-2).

Terms

a(0) =2a(1) =2a(2) =6a(3) =32a(4) =250a(5) =2592a(6) =33614a(7) =524288a(8) =9565938a(9) =200000000a(10) =4715895382a(11) =123834728448