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A060050
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Number of irreducible nonpositively curved triangulations of an n-gon: All internal vertices have at valence at least 6 and no diagonals of the n-gon are allowed.
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0
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0, 1, 0, 0, 1, 1, 5, 13, 46, 155, 561, 2068, 7871, 30586, 121391, 490196, 2011422, 8370698, 35285987, 150485667, 648653910, 2823402675, 12400659846, 54920758496, 245126368841, 1101983749921, 4987538210079, 22716326086134
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,7
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LINKS
| Greg Kuperberg, Spiders for rank 2 Lie algebras, Comm. Math. Phys. 180 (1996), 109-151, arXiv:q-alg/9712003
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FORMULA
| The g.f. C(x) is derived from the g.f. B(x) of A060049 by B_1(x) = C_1(B_1(x))+x, where B_1(x) = B(x)/x and C_1(x) = C(x)/x.
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EXAMPLE
| c(8) = 5 = 1+4. We can divide the octagon into 8 pie slices and we can split any pair of opposite radii of this triangulation into two triangles.
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CROSSREFS
| A060049, A059710.
Sequence in context: A147200 A147396 A099972 * A194639 A152925 A120790
Adjacent sequences: A060047 A060048 A060049 * A060051 A060052 A060053
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KEYWORD
| easy,nonn
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AUTHOR
| Greg Kuperberg (greg(AT)math.ucdavis.edu), Feb 15 2001
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