A161461 Number of reduced words of length n in the Weyl group A_12.

1, 12, 77, 351, 1274, 3914, 10569, 25728, 57486, 119483, 233389, 431886, 762007, 1288587, 2097472, 3298033, 5024460, 7435284, 10710609, 15046642, 20647290, 27712842, 36426054, 46936280, 59342609, 73677240, 89890517, 107839121

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 I.)

Links

Table of n, a(n) for n=0..27.

Formula

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.

Crossrefs

Sequence in context: A190066 A335253 A071767 * A162297 A161858 A054334

Adjacent sequences: A161458 A161459 A161460 * A161462 A161463 A161464

Keyword

nonn

Author

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

Status

approved