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

Author

Jeffrey Shallit, Mar 07 2019

Keywords

• nonn

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.

Examples

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

Crossrefs

Cf. A003000.

Extensions

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