A164777 - OEIS

A164777

Number of reduced words of length n in Coxeter group on 9 generators S_i with relations (S_i)^2 = (S_i S_j)^8 = I.

1, 9, 72, 576, 4608, 36864, 294912, 2359296, 18874332, 150994368, 1207952676, 9663603264, 77308680960, 618468286464, 4947737001984, 39581821698048, 316653979043052, 2533227076022832, 20265778557681300, 162125924058011088

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OFFSET

0,2

COMMENTS

The initial terms coincide with those of A003951, 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 (7, 7, 7, 7, 7, 7, 7, -28).

FORMULA

G.f.: (t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(28*t^8 - 7*t^7 - 7*t^6 - 7*t^5 - 7*t^4 - 7*t^3 - 7*t^2 - 7*t + 1).

CROSSREFS

Sequence in context: A163391 A163953 A164375 * A165216 A165787 A166367

Adjacent sequences: A164774 A164775 A164776 * A164778 A164779 A164780

KEYWORD

nonn

AUTHOR

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

STATUS

approved