a(n) = 3^(n-1)*(3^n - 1), n >= 0.

Terms

a(0) =0a(1) =2a(2) =24a(3) =234a(4) =2160a(5) =19602a(6) =176904a(7) =1593594a(8) =14346720a(9) =129133602a(10) =1162241784a(11) =10460294154a(12) =94143001680a(13) =847288078002