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A348222
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Number of uniquely-3-colorable graphs on n vertices.
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1
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OFFSET
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3,3
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COMMENTS
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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.
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LINKS
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FORMULA
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EXAMPLE
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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.
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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