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A275307
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Number of labeled spanning blobs on n vertices.
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38
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OFFSET
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1,3
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COMMENTS
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A clutter is a set of sets comprising a connected antichain in the Boolean algebra B_n. A blob is defined as a clutter that cannot be capped by a tree.
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LINKS
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FORMULA
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Every clutter is a tree of blobs, so we have A048143(n) = Sum_p n^(k-1) Prod_i a(|p_i|+1), where the sum is over all set partitions U(p_1,...,p_k) = {1,...,n-1}.
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EXAMPLE
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The a(3)=2 blobs are: {{1,2,3}}, {{1,2},{1,3},{2,3}}.
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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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