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A125062
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Number of increasing trees with hills of height 1.
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0
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1, 1, 4, 15, 68, 370, 2364, 17388, 144864, 1349136, 13894560, 156831840, 1925527680, 25550778240, 364416917760, 5559659078400, 90349397913600, 1558170228787200, 28423674336153600, 546807873520742400
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| If we discard the first 1 and set a(0)=1,a(1)=4, then a(n) = (n+1)!(H(n)+1), where H(n) = sum(1/k,k=1..n) [From Gary Detlefs (gdetlefs(AT)aol.com), Jul 21 2010]
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REFERENCES
| R. P. Stanley, Enumerative Combinatorics, Vol. 1, Cambridge University Press, 1997, p25.
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FORMULA
| E.g.f.: (1+x*log(1/(1-x)))/(1-x).
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CROSSREFS
| Sequence in context: A164310 A011967 A055732 * A039625 A020020 A000882
Adjacent sequences: A125059 A125060 A125061 * A125063 A125064 A125065
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KEYWORD
| nonn
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AUTHOR
| Wenjin Woan (wjwoan(AT)hotmail.com), Jan 09 2007
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EXTENSIONS
| Edited by the Associate Editors of the OEIS, Oct 05 2009
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