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A162347 Number of reduced words of length n in the Weyl group D_19. 0
1, 19, 189, 1311, 7124, 32300, 127091, 445721, 1420364, 4172476, 11426240, 29429784, 71808030, 166970290, 371826581, 796341623, 1646167391, 3294638285, 6401307860, 12102626403, 22312161567, 40184022241, 70815180079 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Computed with MAGMA using commands similar to those used to compute A161409.

REFERENCES

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.

LINKS

Table of n, a(n) for n=0..22.

FORMULA

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.

CROSSREFS

Sequence in context: A034273 A193575 A161512 * A161879 A176600 A139619

Adjacent sequences:  A162344 A162345 A162346 * A162348 A162349 A162350

KEYWORD

nonn

AUTHOR

John Cannon and N. J. A. Sloane, Dec 01 2009

STATUS

approved

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Last modified October 14 09:25 EDT 2019. Contains 327995 sequences. (Running on oeis4.)