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Search: id:A001895
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| A001895 |
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Number of rooted planar 2-trees with n nodes.
(Formerly M1258 N0481)
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+0
1
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| 1, 2, 4, 12, 34, 111, 360, 1226, 4206, 14728, 52024, 185824, 668676, 2424033, 8839632, 32412270, 119410390, 441819444, 1641032536, 6116579352, 22870649308, 85764947502, 322476066224, 1215486756372, 4591838372044
(list; graph; listen)
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OFFSET
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1,2
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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).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
Harary, Frank; and Palmer, Edgar M.; On acyclic simplicial complexes. Mathematika 15 1968 115-122.
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 78, (3.5.28).
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..200
Index entries for sequences related to rooted trees
Index entries for sequences related to trees
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FORMULA
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G.f.: (4-8*x^2-sqrt(1-4*x)-(3+2*x)*sqrt(1-4*x^2))/(8*x^2).
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CROSSREFS
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Cf. A000108, A000207.
Sequence in context: A148198 A148199 A108530 this_sequence A148200 A148201 A148202
Adjacent sequences: A001892 A001893 A001894 this_sequence A001896 A001897 A001898
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KEYWORD
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nonn,nice,easy
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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 from Vladeta Jovovic (vladeta(AT)eunet.rs), Aug 24 2001
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