a(n) = (3^n-1)*(3^n+3)/3!.

Terms

a(0) =0a(1) =2a(2) =16a(3) =130a(4) =1120a(5) =9922a(6) =88816a(7) =797890a(8) =7176640a(9) =64576642a(10) =581150416a(11) =5230235650a(12) =47071766560a(13) =423644836162