Number of bifix-free (or primary, or unbordered) words of length n over a two-letter alphabet.

Terms

a(0) =1a(1) =2a(2) =2a(3) =4a(4) =6a(5) =12a(6) =20a(7) =40a(8) =74a(9) =148a(10) =284a(11) =568a(12) =1116a(13) =2232a(14) =4424a(15) =8848a(16) =17622a(17) =35244a(18) =70340a(19) =140680a(20) =281076a(21) =562152a(22) =1123736a(23) =2247472a(24) =4493828a(25) =8987656a(26) =17973080a(27) =35946160a(28) =71887896a(29) =143775792