Number of binary sequences of length n that contain at least one contiguous subsequence 011.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =4a(5) =12a(6) =31a(7) =74a(8) =168a(9) =369a(10) =792a(11) =1672a(12) =3487a(13) =7206a(14) =14788a(15) =30185a(16) =61356a(17) =124308a(18) =251199a(19) =506578a(20) =1019920a(21) =2050785a(22) =4119280a(23) =8267216a(24) =16580799a(25) =33236622a(26) =66594636a(27) =133385689a(28) =267089188a(29) =534692604