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A036361
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Number of labeled 2-trees with n nodes.
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8
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0, 1, 1, 6, 70, 1215, 27951, 799708, 27337500, 1086190605, 49162945645, 2496308717826, 140489907594114, 8678436279296875, 583701359488329915, 42457773984656284920, 3320786296452525792376, 277898747312921495246937, 24775177557380767822265625
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listen;
history;
text;
internal format)
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OFFSET
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1,4
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REFERENCES
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F. Harary and E. Palmer, Graphical Enumeration, (1973), p. 30.
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LINKS
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FORMULA
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Number of labeled k-trees on n nodes is binomial(n, k) * (k(n-k)+1)^(n-k-2).
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MAPLE
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MATHEMATICA
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Table[Binomial[n, 2](2n-3)^(n-4), {n, 20}] (* Harvey P. Dale, Nov 24 2011 *)
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PROG
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(Python)
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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STATUS
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approved
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