A306742 Number of length-n binary words that can be written as the concatenation of two unbordered binary words.

0, 4, 6, 14, 26, 54, 104, 210, 412, 832, 1654, 3330, 6670, 13452, 27004, 54414, 109400, 220264, 442938, 891256, 1791894, 3603128, 7241452, 14552628, 29234478, 58720290, 117911510, 236729446, 475169660, 953616548, 1913446072, 3838773120, 7700145556, 15443494464, 30969376788, 62096345834, 124493833506

Offset

1,2

Comments

A word w is bordered if it has a nonempty prefix, unequal to w, that is also a suffix. A word is unbordered if it is not bordered.

Links

Table of n, a(n) for n=1..37.

Example

For n = 5, the 6 words that are not so expressible are 00000, 00100, 01010, and their complements.

Crossrefs

Cf. A003000.

Sequence in context: A200186 A370410 A192782 * A188576 A084214 A030138

Adjacent sequences: A306739 A306740 A306741 * A306743 A306744 A306745

Keyword

nonn

Author

Jeffrey Shallit, Mar 07 2019

Extensions

a(23)-a(37) from Bert Dobbelaere, Mar 24 2019

Status

approved