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Search: id:A002990
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| A002990 |
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Number of n-node trees with a forbidden limb of length 4.
(Formerly M0350)
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+0
1
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| 1, 1, 1, 1, 2, 2, 5, 9, 19, 38, 86, 188, 439, 1026, 2472, 5997, 14835, 36964, 93246, 236922, 607111, 1565478, 4062797, 10599853, 27797420, 73224806, 193709710, 514406793, 1370937140, 3665714528, 9831891555, 26445886506, 71325268179
(list; graph; listen)
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OFFSET
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0,5
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COMMENT
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A tree with a forbidden limb of length k is a tree where the path from any leaf inward hits a branching node or another leaf within k steps.
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
A. J. Schwenk, Almost all trees are cospectral, pp. 275-307 of F. Harary, editor, New Directions in the Theory of Graphs. Academic Press, NY, 1973.
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LINKS
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Index entries for sequences related to trees
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FORMULA
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G.f.: 1+B(x)+(B(x^2)-B(x)^2)/2 where B(x) is g.f. of A052327.
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CROSSREFS
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Cf. A002955, A002988-A002992, A052318-A052329.
Sequence in context: A076607 A054229 A052969 this_sequence A060405 A003228 A110182
Adjacent sequences: A002987 A002988 A002989 this_sequence A002991 A002992 A002993
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms, formula and comments from Christian G. Bower (bowerc(AT)usa.net), Dec 15 1999.
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