A164627 - OEIS

A164627

Number of reduced words of length n in Coxeter group on 16 generators S_i with relations (S_i)^2 = (S_i S_j)^7 = I.

1, 16, 240, 3600, 54000, 810000, 12150000, 182249880, 2733746400, 41006169120, 615092133600, 9226375956000, 138395548620000, 2075931868500000, 31138957615514280, 467084058053130000, 7006256278106196720

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OFFSET

0,2

COMMENTS

The initial terms coincide with those of A170735, 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..16.

Index entries for linear recurrences with constant coefficients, signature (14,14,14,14,14,14,-105).

FORMULA

G.f.: (t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(105*t^7 - 14*t^6 - 14*t^5 - 14*t^4 - 14*t^3 - 14*t^2 - 14*t + 1).

CROSSREFS

Sequence in context: A163092 A163441 A163964 * A164867 A063814 A165308

Adjacent sequences: A164624 A164625 A164626 * A164628 A164629 A164630

KEYWORD

nonn

AUTHOR

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

STATUS

approved