A163171 Number of reduced words of length n in Coxeter group on 23 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.

1, 23, 506, 11132, 244651, 5376756, 118166433, 2596973148, 57074328696, 1254336803181, 27566873759502, 605844081921771, 13314786972244758, 292622404684911840, 6431035802682200787, 141336482898202575984

Offset

0,2

Comments

The initial terms coincide with those of A170742, although the two sequences are eventually different.

Computed with MAGMA using commands similar to those used to compute A154638.

Links

Table of n, a(n) for n=0..15.

Index entries for linear recurrences with constant coefficients, signature (21,21,21,-231).

Formula

G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(231*t^4 - 21*t^3 - 21*t^2 - 21*t + 1).

Mathematica

CoefficientList[Series[(t^4 + 2 t^3 + 2 t^2 + 2 t + 1)/(231 t^4 - 21 t^3 - 21 t^2 - 21 t + 1), {t, 0, 20}], t] (* Jinyuan Wang, Mar 23 2020 *)

Crossrefs

Sequence in context: A121903 A162809 A212336 * A163518 A163991 A164636

Adjacent sequences: A163168 A163169 A163170 * A163172 A163173 A163174

Keyword

nonn

Author

John Cannon and N. J. A. Sloane, Dec 03 2009

Status

approved