Number of ternary words of length n avoiding the pattern 11-11.

Terms

a(0) =1a(1) =3a(2) =9a(3) =27a(4) =78a(5) =222a(6) =618a(7) =1686a(8) =4512a(9) =11856a(10) =30624a(11) =77856a(12) =195072a(13) =482304a(14) =1178112a(15) =2846208a(16) =6807552a(17) =16134144a(18) =37920768a(19) =88449024a(20) =204865536a(21) =471465984a(22) =1078591488a(23) =2454061056a(24) =5555355648a(25) =12516851712a(26) =28078768128a(27) =62732107776a(28) =139619991552a(29) =309640298496