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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.
0
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.
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
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