Number of rich ternary words of length n.

Terms

a(0) =1a(1) =3a(2) =9a(3) =27a(4) =75a(5) =201a(6) =513a(7) =1269a(8) =3033a(9) =7047a(10) =15903a(11) =35031a(12) =75291a(13) =158487a(14) =326889a(15) =662259a(16) =1318803a(17) =2585931a(18) =4996251a(19) =9524343a(20) =17925495a(21) =33341619a(22) =61324821a(23) =111624927a(24) =201179643a(25) =359232897a(26) =635814867a(27) =1116019719a(28) =1943414733a(29) =3358893675