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A081809
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Number n-cyclic graphs.
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0
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1, 3, 3, 10, 12, 35, 58, 160, 341, 958, 2444, 7242, 21190, 67217, 217335, 740542, 2593802, 9444080, 35383843
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OFFSET
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3,2
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COMMENTS
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Take the graph of an n-cycle and consider all possible contractions (including no contraction at all) that do not produce self-loops. Then eliminate multiple edges and count the nonisomorphic graphs.
n-cyclic graphs are distinct simple graphs on which there exists a closed n-walk.
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LINKS
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EXAMPLE
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a(4)=3 because the square loop gives itself and can be folded to give the tree on three vertices and the connected graph on two vertices:
._.
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CROSSREFS
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KEYWORD
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nonn,nice,more,hard
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AUTHOR
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Timothy K. Callahan (timcall(AT)math.la.asu.edu), Apr 10 2003
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EXTENSIONS
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STATUS
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approved
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