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A245246
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Number of ways to delete an edge (up to the outcome) in the simple unlabeled graphs on n nodes.
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2
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OFFSET
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1,3
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COMMENTS
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Also, the number of distinct pairs (G,H) of simple unlabeled graphs on n nodes, where H can be obtained from G by deletion of a single edge.
For n<6, we have a(n) = A126122(n), since the non-isomorphic edges in a graph on n<6 nodes uniquely define the result of their deletion. However, there is a graph on 6 nodes (see link below) with two non-isomorphic edges, deletion of either of which results in the same graph. Hence, for n>=6, a(n) < A126122(n).
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LINKS
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Table of n, a(n) for n=1..9.
Max Alekseyev, Example of the graph on 6 nodes, where deletion of red or blue edge (which are non-isomorphic) results in the same graph.
Max Alekseyev et al., Removal of non-isomorphic edges results in the same graph, MathOverflow, 2014.
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CROSSREFS
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Cf. A000088, A126122
Sequence in context: A277939 A210346 A074549 * A126122 A303034 A026004
Adjacent sequences: A245243 A245244 A245245 * A245247 A245248 A245249
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KEYWORD
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nonn,more
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AUTHOR
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Max Alekseyev, Jul 15 2014
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STATUS
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approved
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