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A163669
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Number of reduced words of length n in Coxeter group on 40 generators S_i with relations (S_i)^2 = (S_i S_j)^5 = I.
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1
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1, 40, 1560, 60840, 2372760, 92536860, 3608907120, 140746192080, 5489055252720, 214071351558480, 8348712382781940, 325597040159662440, 12698177599143380760, 495224754685478312040, 19313602738540732379160
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OFFSET
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0,2
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COMMENTS
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The initial terms coincide with those of A170759, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.
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LINKS
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FORMULA
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G.f.: (t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(741*t^5 - 38*t^4 - 38*t^3 - 38*t^2 - 38*t + 1).
a(n) = 38*a(n-1)+38*a(n-2)+38*a(n-3)+38*a(n-4)-741*a(n-5). - Wesley Ivan Hurt, May 11 2021
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MATHEMATICA
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CoefficientList[Series[(1+x)*(1-x^5)/(1-39*x+779*x^5-741*x^6), {x, 0, 20}], x] (* G. C. Greubel, Aug 01 2017 *)
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PROG
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(PARI) my(x='x+O('x^20)); Vec((1+x)*(1-x^5)/(1-39*x+779*x^5-741*x^6)) \\ G. C. Greubel, Aug 01 2017
(Magma) R<x>:=PowerSeriesRing(Integers(), 20); Coefficients(R!( (1+x)*(1-x^5)/(1-39*x+779*x^5-741*x^6) )); // G. C. Greubel, May 23 2019
(Sage) ((1+x)*(1-x^5)/(1-39*x+779*x^5-741*x^6)).series(x, 20).coefficients(x, sparse=False) # G. C. Greubel, May 23 2019
(GAP) a:=[40, 1560, 60840, 2372760, 92536860];; for n in [6..20] do a[n]:=38*(a[n-1]+a[n-2] +a[n-3]+a[n-4]) -741*a[n-5]; od; Concatenation([1], a); # G. C. Greubel, May 23 2019
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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