A163084 Number of reduced words of length n in Coxeter group on 13 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.

1, 13, 156, 1872, 22386, 267696, 3201198, 38280528, 457766166, 5474058876, 65459882202, 782782264836, 9360665698098, 111936698410680, 1338561257884422, 16006781212446024, 191412266920077918, 2288945881199387124, 27371669179630649874, 327315853045229826492

Offset

0,2

Comments

The initial terms coincide with those of A170732, 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..19.

Index entries for linear recurrences with constant coefficients, signature (11, 11, 11, -66).

Formula

G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(66*t^4 - 11*t^3 - 11*t^2 - 11*t + 1).

Mathematica

CoefficientList[Series[(t^4+2t^3+2t^2+2t+1)/(66t^4-11t^3-11t^2- 11t+1), {t, 0, 30}], t] (* Harvey P. Dale, Jun 19 2011 *)

Crossrefs

Sequence in context: A102146 A162768 A097827 * A163438 A163958 A164610

Adjacent sequences: A163081 A163082 A163083 * A163085 A163086 A163087

Keyword

nonn

Author

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

Extensions

More terms from Harvey P. Dale, Jun 19 2011

Status

approved