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A161512
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Number of reduced words of length n in the Weyl group A_19.
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0
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1, 19, 189, 1310, 7105, 32110, 125761, 438407, 1386735, 4038090, 10947079, 27876345, 67163518, 154022930, 337879565, 712033264, 1446677555, 2842707951, 5417028610, 10034398370, 18106447251, 31885534341, 54889773721, 92505945904
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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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J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge, 1990. See under Poincaré polynomial.
N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche I.)
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LINKS
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FORMULA
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G.f. for A_m is the polynomial Prod_{k=1..m}(1-x^(k+1))/(1-x). Only finitely many terms are nonzero. This is a row of the triangle in A008302.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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