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A161733
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Number of reduced words of length n in the Weyl group B_9.
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0
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1, 9, 44, 156, 449, 1113, 2463, 4983, 9372, 16588, 27886, 44846, 69387, 103763, 150538, 212538, 292779, 394371, 520399, 673783, 857121, 1072521, 1321430, 1604470, 1921291, 2270451, 2649332, 3054100, 3479715, 3919995, 4367735
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Computed with MAGMA using commands similar to those used to compute A161409.
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REFERENCES
| J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge, 1990. See under Poincare polynomial.
N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche II.)
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FORMULA
| G.f. for B_m is the polynomial Prod_{k=1..m}(1-x^(2k))/(1-x). Only finitely many terms are nonzero. This is a row of the triangle in A128084.
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CROSSREFS
| Sequence in context: A075206 A161457 A162212 * A050486 A036599 A059825
Adjacent sequences: A161730 A161731 A161732 * A161734 A161735 A161736
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KEYWORD
| nonn
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AUTHOR
| John Cannon (john(AT)maths.usyd.edu.au) and N. J. A. Sloane (njas(AT)research.att.com), Nov 30 2009
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