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A006860
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Tiered orders on n nodes.
(Formerly M2959)
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2
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1, 3, 13, 111, 1381, 25623, 678133, 26269735, 1447451707, 114973020921, 13034306495563
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Graded posets, i.e., those in which every maximal chain has the same length. (The terminology "graded" is also used to refer to a weaker notion; see A001833.)
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REFERENCES
| G. Kreweras, Dénombrement des ordres étagés, Discrete Math., 53 (1985), 147-149.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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CROSSREFS
| Sequence in context: A073587 A061377 A183604 * A181083 A090537 A063269
Adjacent sequences: A006857 A006858 A006859 * A006861 A006862 A006863
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KEYWORD
| nonn
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AUTHOR
| Simon Plouffe (simon.plouffe(AT)gmail.com)
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