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A316500
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Number of unlabeled rooted identity trees with n nodes in which the branches of any node with more than one branch have empty intersection.
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6
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1, 1, 1, 2, 3, 6, 11, 22, 46, 96, 205, 442, 976, 2146, 4789, 10719, 24202, 54841, 124967, 285724, 656011, 1510929, 3491151, 8088692, 18790084
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OFFSET
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1,4
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LINKS
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EXAMPLE
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The a(7) = 11 rooted identity trees:
((((((o))))))
((((o(o)))))
(((o((o)))))
((o(((o)))))
((o(o(o))))
(((o)((o))))
(o((((o)))))
(o((o(o))))
(o(o((o))))
((o)(((o))))
(o(o)((o)))
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MATHEMATICA
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strut[n_]:=strut[n]=If[n===1, {{}}, Select[Join@@Function[c, Union[Sort/@Tuples[strut/@c]]]/@IntegerPartitions[n-1], UnsameQ@@#&&Or[Length[#]==1, Intersection@@#=={}]&]];
Table[Length[strut[n]], {n, 20}]
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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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