%I #6 Mar 05 2020 22:51:29
%S 0,2,2,4,6,12,18,34,54,100,170,310,542,1000,1786,3292,5990,11100,
%T 20434,38102,70858,132912,249290,470300,888158,1684488,3199258,
%U 6095502,11631550,22249232,42621834,81804946,157221374,302632804,583237734,1125468466,2174144774
%N Number of length-n binary words closed by an unbordered word.
%C 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.
%e For n = 5 the a(5) = 6 words counted are 01001, 01101, 01110, and their binary complements.
%Y Counts a subset of A226452.
%K nonn
%O 1,2
%A _Jeffrey Shallit_, Mar 05 2020