1,2

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.

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

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

Counts a subset of A226452.

Sequence in context: A267610 A291365 A154779 * A010101 A274942 A028408

Adjacent sequences: A332980 A332981 A332982 * A332984 A332985 A332986

nonn

Jeffrey Shallit, Mar 05 2020

approved