A163187 Number of reduced words of length n in Coxeter group on 28 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.

1, 28, 756, 20412, 550746, 14859936, 400943088, 10818033408, 291886435386, 7875524871396, 212493231821052, 5733379591597476, 154695004916717538, 4173898512013677720, 112617914185202621832, 3038596784018807730264

Offset: 0

Author

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

Keywords

• nonn

Comments

The initial terms coincide with those of A170747, 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 (26,26,26,-351).

Programs

Mathematica

coxG[{4,351,-26}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Jul 05 2017 *)

PARI

Vec((t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(351*t^4 - 26*t^3 - 26*t^2 - 26*t + 1) + O(t^20)) \\ Jinyuan Wang, Mar 23 2020

Formula

G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(351*t^4 - 26*t^3 - 26*t^2 - 26*t + 1).