A161523 Number of reduced words of length n in the Weyl group A_23.

1, 23, 275, 2276, 14650, 78131, 359214, 1462801, 5380529, 18142125, 56724395, 165980490, 457927079, 1198603761, 2991929700, 7153857324, 16447016616, 36476745510, 78265410550, 162869776650, 329453055975, 649063995030

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..21.

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: A142220 A257930 A142027 * A161930 A162365 A162680

Adjacent sequences: A161520 A161521 A161522 * A161524 A161525 A161526

Keyword

nonn

Author

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

Status

approved