a(n) = (n-1)*3^(n-2), n > 0.

Terms

a(0) =0a(1) =1a(2) =6a(3) =27a(4) =108a(5) =405a(6) =1458a(7) =5103a(8) =17496a(9) =59049a(10) =196830a(11) =649539a(12) =2125764a(13) =6908733a(14) =22320522a(15) =71744535a(16) =229582512a(17) =731794257a(18) =2324522934a(19) =7360989291a(20) =23245229340a(21) =73222472421a(22) =230127770466a(23) =721764371007