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%I #12 Jan 17 2024 09:07:46
%S 1,1,3,12,72,856,17018,531568
%N Number of uniquely-3-colorable graphs on n vertices.
%C A graph is uniquely 3-colorable if there is a unique partition of its vertex set into 3 independent sets. This implies that every proper 3-coloring of the graph has this partition as its set of color classes.
%F a(n) = A369227(n,3). - _Eric W. Weisstein_, Jan 16 2024
%e a(3) = 1 and a(4) = 1 because the complete graph K3 and K4-e are the only such graphs on 3 and 4 vertices, respectively.
%Y Cf. A369227
%K nonn,more
%O 3,3
%A _Gordon Royle_, Oct 08 2021