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Search: id:A140983
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| A140983 |
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Egf is reversion of (2(1+x)log(1+x)+x^2+2x)/( (2+x)^2(1+x) ). |
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| 1, 3, 17, 145, 1663, 24031, 419521, 8592417, 202069759, 5367258479, 158934860321, 5191969220945, 185490468312767, 7194912503747775, 301130097048242561, 13526711564792340289, 649121580063333263359, 33142745983169890692559
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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a(n) is the number of labeled incomplete ternary trees on n vertices in which each left or middle child has a larger label than its parent and each right child has a smaller label than its parent. For example, a(2)=3 because we have 2L1, 2M1 and 1R2. Here aLb means a is a left child of b, etc.
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MAPLE
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N:= 8: exp(RootOf(2*_Z*exp(_Z)-x*exp(_Z)-2*x*exp(_Z)^2-x*exp(_Z)^3-1+exp(_Z)^2))-1: series(%, x, N+1): convert(%, polynom): seq( i!*coeff(%, x, i), i=1..N);
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CROSSREFS
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Cf. A007889.
Sequence in context: A051442 A162650 A015735 this_sequence A138013 A052807 A080253
Adjacent sequences: A140980 A140981 A140982 this_sequence A140984 A140985 A140986
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KEYWORD
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easy,nonn
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AUTHOR
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Brian Drake (bdrake(AT)brandeis.edu), Jul 28 2008
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