A332983 Number of length-n binary words closed by an unbordered word.

0, 2, 2, 4, 6, 12, 18, 34, 54, 100, 170, 310, 542, 1000, 1786, 3292, 5990, 11100, 20434, 38102, 70858, 132912, 249290, 470300, 888158, 1684488, 3199258, 6095502, 11631550, 22249232, 42621834, 81804946, 157221374, 302632804, 583237734, 1125468466, 2174144774

Offset: 1

Author

Jeffrey Shallit, Mar 05 2020

Keywords

• nonn

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.

Examples

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

Crossrefs

Counts a subset of A226452.