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

0,2

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

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

Index entries for linear recurrences with constant coefficients, signature (26,26,26,-351).

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).

Mathematica

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

Prog

(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

Crossrefs

Sequence in context: A229463 A097834 A162830 * A163548 A164025 A164664

Adjacent sequences: A163184 A163185 A163186 * A163188 A163189 A163190

Keyword

nonn

Author

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

Status

approved