A164780 Number of reduced words of length n in Coxeter group on 11 generators S_i with relations (S_i)^2 = (S_i S_j)^8 = I.

1, 11, 110, 1100, 11000, 110000, 1100000, 11000000, 109999945, 1099998900, 10999983555, 109999781100, 1099997266500, 10999967220000, 109999617750000, 1099995633000000, 10999950885002970, 109999454400086625

Offset

0,2

Comments

The initial terms coincide with those of A003953, 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..17.

Index entries for linear recurrences with constant coefficients, signature (9, 9, 9, 9, 9, 9, 9, -45).

Formula

G.f.: (t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(45*t^8 - 9*t^7 - 9*t^6 - 9*t^5 - 9*t^4 - 9*t^3 - 9*t^2 - 9*t + 1).

Mathematica

coxG[{8, 45, -9}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Feb 10 2019 *)

Crossrefs

Sequence in context: A164590 A115806 A115830 * A165264 A165796 A166369

Adjacent sequences: A164777 A164778 A164779 * A164781 A164782 A164783

Keyword

nonn

Author

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

Status

approved