Number of binary strings of length n avoiding substrings 1000, 1011, 1101, or 1111.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =12a(5) =18a(6) =27a(7) =41a(8) =61a(9) =88a(10) =129a(11) =189a(12) =276a(13) =401a(14) =582a(15) =848a(16) =1233a(17) =1791a(18) =2601a(19) =3779a(20) =5492a(21) =7976a(22) =11584a(23) =16826a(24) =24441a(25) =35500a(26) =51558a(27) =74885a(28) =108767a(29) =157976