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A162413
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Number of reduced words of length n in the Weyl group D_44.
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0
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1, 44, 989, 15136, 177374, 1697080, 13804461, 98156916, 622600869, 3577478696, 18848352755, 91943892924, 418593879770, 1790510819500, 7236416033496, 27766992285908, 101579448507141, 355579239690840, 1194844427708580
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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: A035611 A161679 A162182 * A010996 A295251 A295650
Adjacent sequences: A162410 A162411 A162412 * A162414 A162415 A162416
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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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