A164665 - OEIS

A164665

Number of reduced words of length n in Coxeter group on 29 generators S_i with relations (S_i)^2 = (S_i S_j)^7 = I.

1, 29, 812, 22736, 636608, 17825024, 499100672, 13974818410, 391294904112, 10956256997238, 306775187021520, 8589704987370528, 240511732667877888, 6734328319302667776, 188561187469333295694, 5279713095949377473052

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OFFSET

0,2

COMMENTS

The initial terms coincide with those of A170748, 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..15.

Index entries for linear recurrences with constant coefficients, signature (27,27,27,27,27,27,-378).

FORMULA

G.f.: (t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(378*t^7 - 27*t^6 - 27*t^5 - 27*t^4 - 27*t^3 - 27*t^2 - 27*t + 1).

MATHEMATICA

coxG[{7, 378, -27}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Aug 19 2019 *)

CROSSREFS

Sequence in context: A163207 A163549 A164026 * A164974 A165512 A166004

Adjacent sequences: A164662 A164663 A164664 * A164666 A164667 A164668

KEYWORD

nonn

AUTHOR

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

STATUS

approved