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A161878
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Number of reduced words of length n in the Weyl group B_18.
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0
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1, 18, 170, 1122, 5813, 25176, 94791, 318630, 974643, 2752112, 7253764, 18003544, 42378246, 95162260, 204856291, 424515042, 849825768, 1648470894, 3106669575, 5701318544, 10209535182, 17871860844, 30631158960, 51476623220, 84931612739
(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: A126539 A161499 A162346 * A139618 A162638 A010970
Adjacent sequences: A161875 A161876 A161877 * A161879 A161880 A161881
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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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