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Search: id:A089433
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| A089433 |
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Number of noncrossing connected graphs on n nodes having exactly two interior faces. |
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+0
1
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| 2, 30, 315, 2856, 23940, 191268, 1480050, 11196900, 83304936, 611931320, 4450217772, 32104210320, 230080173960, 1639890119016, 11634355574100, 82216112723640, 579022013389050, 4065827626164150, 28475852003986695
(list; graph; listen)
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OFFSET
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4,1
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REFERENCES
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P. Flajolet and M. Noy, Analytic combinatorics of non-crossing configurations, Discrete Math. 204 (1999), 203-229.
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FORMULA
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a(n)=n*binomial(3n-3, n-4)/2.
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EXAMPLE
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a(4)=2 because the only connected graphs on the nodes A,B,C,D having exactly two interior faces are {AB,BC,CD,DA,AC} and {AB,BC,CD,DA,BD}.
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CROSSREFS
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Cf. A007297.
Sequence in context: A157054 A092355 A036351 this_sequence A152277 A083446 A091345
Adjacent sequences: A089430 A089431 A089432 this_sequence A089434 A089435 A089436
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch (deutsch(AT)duke.poly.edu), Dec 28 2003
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