A167956 Number of reduced words of length n in Coxeter group on 40 generators S_i with relations (S_i)^2 = (S_i S_j)^16 = I.
1, 40, 1560, 60840, 2372760, 92537640, 3608967960, 140749750440, 5489240267160, 214080370419240, 8349134446350360, 325616243407664040, 12699033492898897560, 495262306223057004840, 19315229942699223188760
Offset: 0
Keywords
Links
- G. C. Greubel, Table of n, a(n) for n = 0..500
- Index entries for linear recurrences with constant coefficients, signature (38,38,38,38,38,38,38,38,38,38,38,38,38,38,38,-741).
Programs
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Magma
R
:=PowerSeriesRing(Integers(), 40); Coefficients(R!( (1+x)*(1-x^16)/(1-39*x+779*x^16-741*x^17) )); // G. C. Greubel, Jul 14 2023 -
Mathematica
CoefficientList[Series[(1+t)*(1-t^16)/(1-39*t+779*t^16-741*t^17), {t, 0, 40}], t] (* G. C. Greubel, Jul 02 2016; Jul 14 2023 *) coxG[{16,741,-38}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Jun 22 2019 *)
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SageMath
def A167956_list(prec): P.
= PowerSeriesRing(ZZ, prec) return P( (1+x)*(1-x^16)/(1-39*x+779*x^16-741*x^17) ).list() A167956_list(40) # G. C. Greubel, Jul 14 2023
Formula
G.f.: (t^16 + 2*t^15 + 2*t^14 + 2*t^13 + 2*t^12 + 2*t^11 + 2*t^10 + 2*t^9 + 2*t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/( 741*t^16 - 38*t^15 - 38*t^14 - 38*t^13 - 38*t^12 - 38*t^11 - 38*t^10 - 38*t^9 - 38*t^8 - 38*t^7 - 38*t^6 - 38*t^5 - 38*t^4 - 38*t^3 - 38*t^2 - 38*t + 1).
From G. C. Greubel, Jul 14 2023: (Start)
G.f.: (1 + t)*(1 - t^16)/(1 - 39*t + 779*t^16 - 741*t^17).
a(n) = -741*a(n-16) + 38*Sum_{j=1..15} a(n-j). (End)
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