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A046715
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Secondary root edges in doubly rooted tree maps with n edges.
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1
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0, 1, 10, 105, 1176, 13860, 169884, 2147145, 27810640, 367479684, 4936848280, 67255063876, 927192688800, 12914469594000, 181497968832600, 2570903476583625, 36671501616314400, 526348636137670500, 7597019633665077000, 110205019733436728100
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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REFERENCES
| R. C. Mullin, On the average activity of a spanning tree of a rooted map, J. Combin. Theory, 3 (1967), 103-121.
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LINKS
| Alois P. Heinz, Table of n, a(n) for n = 0..250
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FORMULA
| B(n) = (2*n)!*(2*n+2)!*n / (2*n!*(n+1)!^2*(n+2)!). - Alois P. Heinz, Dec 22 2011
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MAPLE
| B:= n-> (2*n)!*(2*n+2)!*n / (2*n!*(n+1)!^2*(n+2)!):
seq (B(n), n=0..20); # Alois P. Heinz, Dec 22 2011
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CROSSREFS
| Sequence in context: A004343 A163166 A068767 * A145713 A123512 A079515
Adjacent sequences: A046712 A046713 A046714 * A046716 A046717 A046718
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| Corrected and extended by Alois P. Heinz (heinz(AT)hs-heilbronn.de), Dec 22 2011
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