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A165214 Number of reduced words of length n in Coxeter group on 7 generators S_i with relations (S_i)^2 = (S_i S_j)^9 = I. 0
1, 7, 42, 252, 1512, 9072, 54432, 326592, 1959552, 11757291, 70543620, 423260985, 2539561500, 15237342540, 91423896480, 548542426320, 3291248842560, 19747458763200, 118484546826660, 710906046446925, 4265428871616150 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The initial terms coincide with those of A003949, 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..20.

Index entries for linear recurrences with constant coefficients, signature (5, 5, 5, 5, 5, 5, 5, 5, -15).

FORMULA

G.f. (t^9 + 2*t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t +

1)/(15*t^9 - 5*t^8 - 5*t^7 - 5*t^6 - 5*t^5 - 5*t^4 - 5*t^3 - 5*t^2 - 5*t

+ 1)

MATHEMATICA

coxG[{9, 15, -5}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Nov 02 2015 *)

CROSSREFS

Sequence in context: A163923 A164369 A164742 * A165782 A166365 A166518

Adjacent sequences: A165211 A165212 A165213 * A165215 A165216 A165217

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified January 29 01:41 EST 2023. Contains 359905 sequences. (Running on oeis4.)