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

Author

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

Keywords

• nonn

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

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

Programs

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 *)

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).

Extensions

More terms from Harvey P. Dale, Jun 19 2011