A164686 - OEIS

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A164686

Number of reduced words of length n in Coxeter group on 42 generators S_i with relations (S_i)^2 = (S_i S_j)^7 = I.

1, 42, 1722, 70602, 2894682, 118681962, 4865960442, 199504377261, 8179679432400, 335366855281920, 13750041007253040, 563751678865841760, 23113818733806664080, 947666563998666456000, 38854328956361647813980

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OFFSET

0,2

COMMENTS

The initial terms coincide with those of A170761, 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..14.

Index entries for linear recurrences with constant coefficients, signature (40,40,40,40,40,40,-820).

FORMULA

G.f.: (t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(820*t^7 - 40*t^6 - 40*t^5 - 40*t^4 - 40*t^3 - 40*t^2 - 40*t + 1).

CROSSREFS