a(n) = n^(n-1) * (n+1)^n.A258384a(n) = n^(n-1) * (n+1)^n.Terms a(0) =2a(1) =18a(2) =576a(3) =40000a(4) =4860000a(5) =914838624a(6) =246727835648External referencesoeis: A258384