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A162402
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Number of reduced words of length n in the Weyl group D_40.
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0
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1, 40, 819, 11440, 122589, 1074488, 8020830, 52427192, 306189025, 1622495952, 7895219982, 35623107520, 150221110689, 595982725640, 2237008815175, 7981961442768, 27186526166255, 88708246063240, 278172606877930
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OFFSET
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0,2
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COMMENTS
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Computed with MAGMA using commands similar to those used to compute A161409.
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REFERENCES
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N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche IV.)
J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge, 1990. See under Poincaré polynomial.
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LINKS
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Table of n, a(n) for n=0..18.
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FORMULA
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G.f. for D_m is the polynomial f(n) * Product( f(2i), i=1..n-1 )/ f(1)^n, where f(k) = 1-x^k. Only finitely many terms are nonzero. This is a row of the triangle in A162206.
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CROSSREFS
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Sequence in context: A035609 A161653 A162176 * A010992 A250584 A004421
Adjacent sequences: A162399 A162400 A162401 * A162403 A162404 A162405
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KEYWORD
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nonn
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AUTHOR
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John Cannon and N. J. A. Sloane, Dec 01 2009
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STATUS
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approved
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