Number of ternary words of length n with no 000's.

Terms

a(0) =1a(1) =3a(2) =9a(3) =26a(4) =76a(5) =222a(6) =648a(7) =1892a(8) =5524a(9) =16128a(10) =47088a(11) =137480a(12) =401392a(13) =1171920a(14) =3421584a(15) =9989792a(16) =29166592a(17) =85155936a(18) =248624640a(19) =725894336a(20) =2119349824a(21) =6187737600a(22) =18065963520a(23) =52746101888a(24) =153999606016a(25) =449623342848