A164628 - OEIS

A164628

Number of reduced words of length n in Coxeter group on 17 generators S_i with relations (S_i)^2 = (S_i S_j)^7 = I.

1, 17, 272, 4352, 69632, 1114112, 17825792, 285212536, 4563398400, 73014339720, 1168228880640, 18691653212160, 299066309345280, 4785058676736000, 76560902463178680, 1224973857577579200, 19599572411913213000

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OFFSET

0,2

COMMENTS

The initial terms coincide with those of A170736, 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 (15,15,15,15,15,15,-120).

FORMULA

G.f.: (t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(120*t^7 - 15*t^6 - 15*t^5 - 15*t^4 - 15*t^3 - 15*t^2 - 15*t + 1).

MATHEMATICA

coxG[{7, 120, -15}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Nov 13 2015 *)

CROSSREFS

Sequence in context: A163093 A163451 A163965 * A164868 A165321 A165879

Adjacent sequences: A164625 A164626 A164627 * A164629 A164630 A164631

KEYWORD

nonn

AUTHOR

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

STATUS

approved