%I #9 Nov 03 2024 19:52:23
%S 4,15,122,5922
%N Number of distinct subsets of length-n words that can be the set of all length-n blocks occurring in some binary word.
%C Another way to say this is that a(n) is the number of distinct sets of vertices of the de Bruijn graph of order n encountered by some walk on the graph.
%e For n = 2, the only set not counted is {00,11}, since if a word has 00 and 11 as blocks appearing in it, then it must have either 01 or 10 also.
%Y Cf. A324149.
%K nonn,more
%O 1,1
%A _Jeffrey Shallit_, Sep 05 2024