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Search: id:A006081
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| A006081 |
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Number of line-rooted projective plane trees with n nodes.
(Formerly M2593)
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+0
3
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| 1, 1, 3, 6, 17, 44, 133, 404, 1319, 4392, 15114, 52796, 187410, 671848, 2430509, 8852584, 32438603, 119463056, 441926206, 1641246060, 6117011262, 22871513128, 85766691938, 322479555096, 1215493792902, 4591852445104, 17383416640308
(list; graph; listen)
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OFFSET
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2,3
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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).
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
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Index entries for sequences related to trees
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FORMULA
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Stockmeyer gives g.f.
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MAPLE
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b:= proc(n) option remember; binomial (n, floor (n/2)) end: c:= proc(n) option remember; binomial (2*n, n) /(n+1) end: a:= proc(m) local n; n:=m-2; (add (c(k)*c(n-k) +b(k)*b(n-k), k=0..n)) /4 +`if` (irem(n, 2)=0, c(n/2)/2, 0) end: seq (a(n), n=2..30); [From Alois P. Heinz (heinz(AT)hs-heilbronn.de), Feb 03 2009]
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CROSSREFS
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Cf. A000108, A001405. [From Alois P. Heinz (heinz(AT)hs-heilbronn.de), Feb 03 2009]
Sequence in context: A121399 A129905 A143363 this_sequence A099511 A143093 A117712
Adjacent sequences: A006078 A006079 A006080 this_sequence A006082 A006083 A006084
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KEYWORD
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nonn,easy,nice
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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 Alois P. Heinz (heinz(AT)hs-heilbronn.de), Feb 03 2009
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