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A006082
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Number of labeled projective plane trees (or "flat" trees) with n nodes.
(Formerly M0798)
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2
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1, 1, 1, 2, 3, 6, 12, 27, 65, 175, 490, 1473, 4588, 14782, 48678, 163414, 555885, 1913334, 6646728, 23278989, 82100014, 291361744, 1039758962, 3729276257, 13437206032, 48620868106
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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REFERENCES
| D. Feldman, ``Counting plane trees,'' preprint, 1992.
R. W. Robinson, personal communication.
R. W. Robinson, Efficiency of power series operations for graph counting, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1982.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
P. K. Stockmeyer, The charm bracelet problem and its applications, pp. 339-349 of Graphs and Combinatorics (Washington, Jun 1973), Ed. by R. A. Bari and F. Harary. Lect. Notes Math., Vol. 406. Springer-Verlag, 1974.
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LINKS
| Index entries for sequences related to trees
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FORMULA
| Equals A006080(n) - A006081(n) + C(2n), C= A000108 [Stockmeyer].
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CROSSREFS
| Cf. A006079, A006080, A006081.
Sequence in context: A061343 A057649 A104872 * A122889 A014280 A073431
Adjacent sequences: A006079 A006080 A006081 * A006083 A006084 A006085
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| a(25) and a(26) from R. W. Robinson, Oct 17 2006
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