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Search: id:A011800
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| A011800 |
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Number of labeled forests of n nodes each component of which is a path. |
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+0
1
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| 1, 1, 2, 7, 34, 206, 1486, 12412, 117692, 1248004, 14625856, 187638716, 2614602112, 39310384192, 634148436104, 10923398137576, 200069534481616, 3882002527006352, 79535575126745632, 1715658099715217584
(list; graph; listen)
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OFFSET
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0,3
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REFERENCES
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R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.15(d).
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LINKS
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T. D. Noe, Table of n, a(n) for n=0..100
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FORMULA
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E.g.f.: exp[ x+x^2/(2(1-x)) ].
a(n) = Sum_{k=0..n} |Stirling1(n, k)|*A003724(k). - Vladeta Jovovic (vladeta(AT)eunet.rs), Oct 19 2003
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MATHEMATICA
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Function[ esl, esl*Array[ Factorial, Length[ esl ], 0 ] ][ CoefficientList[ Series[ Exp[ x+x^2/(2-2x) ], {x, 0, 20} ], x ] ] (from Olivier Gerard).
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CROSSREFS
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Sequence in context: A145345 A056543 A075834 this_sequence A112916 A145845 A002720
Adjacent sequences: A011797 A011798 A011799 this_sequence A011801 A011802 A011803
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KEYWORD
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nonn,easy,nice
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AUTHOR
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Herbert S. Wilf (wilf(AT)math.upenn.edu)
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