Number of ternary (0,1,2) sequences without a consecutive '012'.

Terms

a(0) =1a(1) =3a(2) =9a(3) =26a(4) =75a(5) =216a(6) =622a(7) =1791a(8) =5157a(9) =14849a(10) =42756a(11) =123111a(12) =354484a(13) =1020696a(14) =2938977a(15) =8462447a(16) =24366645a(17) =70160958a(18) =202020427a(19) =581694636a(20) =1674922950a(21) =4822748423a(22) =13886550633a(23) =39984728949a(24) =115131438424a(25) =331507764639