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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
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 Poincaré polynomial.
N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche II.)
LINKS
FORMULA
G.f. for B_m is the polynomial Product_{k=1..m}(1-x^(2k))/(1-x). Only finitely many terms are nonzero. This is a row of the triangle in A128084.
MAPLE
G:= normal(mul((1-x^(2*k))/(1-x), 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
KEYWORD
nonn,fini,full
AUTHOR
John Cannon and N. J. A. Sloane, Nov 30 2009
STATUS
approved