Total number of different letters summed over all ternary words of length n.

Terms

a(0) =0a(1) =3a(2) =15a(3) =57a(4) =195a(5) =633a(6) =1995a(7) =6177a(8) =18915a(9) =57513a(10) =174075a(11) =525297a(12) =1582035a(13) =4758393a(14) =14299755a(15) =42948417a(16) =128943555a(17) =387027273a(18) =1161475035a(19) =3485211537a(20) =10457207475a(21) =31374768153a(22) =94130595915a(23) =282404370657a(24) =847238277795