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

Author

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

Keywords

• nonn

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

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

Programs

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 *)

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).