Number of ternary words with exactly one 012.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =6a(5) =27a(6) =106a(7) =387a(8) =1350a(9) =4566a(10) =15102a(11) =49113a(12) =157622a(13) =500520a(14) =1575558a(15) =4923536a(16) =15290784a(17) =47235771a(18) =145246224a(19) =444814533a(20) =1357368786a(21) =4128880561a(22) =12523521786a(23) =37888119522a(24) =114358226428a(25) =344437708131