

A306742


Number of lengthn binary words that can be written as the concatenation of two unbordered binary words.


0



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
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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: A175722 A200186 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



