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Search: id:A002989
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| A002989 |
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Number of n-node trees with a forbidden limb of length 3.
(Formerly M1082)
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+0
2
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| 1, 1, 1, 1, 1, 2, 4, 7, 14, 28, 61, 131, 297, 678, 1592, 3770, 9096, 22121, 54451, 135021, 337651, 849698, 2152048, 5479408, 14022947, 36048514, 93061268, 241160180, 627179689, 1636448181, 4282964600, 11241488853, 29584389474
(list; graph; listen)
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OFFSET
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0,6
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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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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 A050321.
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CROSSREFS
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Cf. A002955, A002988-A002992, A052318-A052329.
Adjacent sequences: A002986 A002987 A002988 this_sequence A002990 A002991 A002992
Sequence in context: A119341 A119342 A119268 this_sequence A000671 A120262 A013326
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KEYWORD
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nonn
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AUTHOR
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njas
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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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