

A161875


Number of reduced words of length n in the Weyl group B_15.


1



1, 15, 119, 665, 2939, 10933, 35580, 103972, 277950, 689282, 1602727, 3523945, 7376794, 14784390, 28500705, 53054703, 95687255, 167682425, 286219155, 476896733, 777117381, 1240541355, 1942863430, 2989193690, 4523359115
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OFFSET

0,2


COMMENTS

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


REFERENCES

J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge, 1990. See under PoincarĂ© polynomial.
N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche II.)


LINKS

Robert Israel, Table of n, a(n) for n = 0..225


FORMULA

G.f. for B_m is the polynomial Product_{k=1..m}(1x^(2k))/(1x). Only finitely many terms are nonzero. This is a row of the triangle in A128084.


MAPLE

G:= normal(mul((1x^(2*k))/(1x), k=1..15)):
seq(coeff(G, x, j), j=0..15^2); # Robert Israel, Nov 26 2017


CROSSREFS

Sequence in context: A253804 A161476 A162321 * A259746 A139615 A196506
Adjacent sequences: A161872 A161873 A161874 * A161876 A161877 A161878


KEYWORD

nonn,fini,full


AUTHOR

John Cannon and N. J. A. Sloane, Nov 30 2009


STATUS

approved



