OFFSET

1,2

COMMENTS

A word is unbordered if it has no nontrivial prefix that is a suffix. A word x is closed by a word y if y has exactly two occurrences in x, one as a prefix, and one as a suffix.

EXAMPLE

For n = 5 the a(5) = 6 words counted are 01001, 01101, 01110, and their binary complements.

CROSSREFS

KEYWORD

nonn

AUTHOR

Jeffrey Shallit, Mar 05 2020

STATUS

approved