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Search: id:A080687
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| A080687 |
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Number of labeled n-element posets with no 3-element antichain. |
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+0
1
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| 1, 1, 3, 18, 174, 2370, 41850, 908460, 23393160, 696752280, 23558056200, 891259815600, 37298874135600, 1710662148795600, 85319825069278800, 4597474487169564000, 266164417718126928000, 16475817276720193392000
(list; graph; listen)
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OFFSET
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0,3
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REFERENCES
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Graham Brightwell and Sarah Goodall, The number of partial orders of fixed width, Order, 13 (1996), 315-337.
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FORMULA
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E.g.f. (3-2*x-sqrt(1-4*x))/(2-2*x+x^2).
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CROSSREFS
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Cf. A006251 for the unlabeled analogue.
Sequence in context: A099716 A113130 A005192 this_sequence A111465 A108994 A006472
Adjacent sequences: A080684 A080685 A080686 this_sequence A080688 A080689 A080690
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KEYWORD
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nonn
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AUTHOR
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Detlef Pauly (dettodet(AT)yahoo.de), Mar 03 2003
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