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

Terms

a(0) =2a(1) =9a(2) =36a(3) =135a(4) =486a(5) =1701a(6) =5832a(7) =19683a(8) =65610a(9) =216513a(10) =708588a(11) =2302911a(12) =7440174a(13) =23914845a(14) =76527504a(15) =243931419a(16) =774840978a(17) =2453663097a(18) =7748409780a(19) =24407490807a(20) =76709256822a(21) =240588123669a(22) =753145430616