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A164027
Number of reduced words of length n in Coxeter group on 30 generators S_i with relations (S_i)^2 = (S_i S_j)^6 = I.
1
1, 30, 870, 25230, 731670, 21218430, 615334035, 17844674400, 517495192200, 15007349977200, 435212842037400, 12621163507344000, 366013483272687390, 10614383520144862920, 307816904736225416280, 8926683934263695000520
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A170749, although the two sequences are eventually different.
Computed with Magma using commands similar to those used to compute A154638.
FORMULA
G.f.: (t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(406*t^6 - 28*t^5 - 28*t^4 - 28*t^3 - 28*t^2 - 28*t + 1).
a(n) = -406*a(n-6) + 28*Sum_{k=1..5} a(n-k). - Wesley Ivan Hurt, May 11 2021
MAPLE
seq(coeff(series((1+t)*(1-t^6)/(1-29*t+434*t^6-406*t^7), t, n+1), t, n), n = 0 .. 30); # G. C. Greubel, Aug 10 2019
MATHEMATICA
CoefficientList[Series[(1+t)*(1-t^6)/(1-29*t+434*t^6-406*t^7), {t, 0, 30}], t] (* G. C. Greubel, Sep 07 2017 *)
coxG[{6, 406, -28}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Jul 05 2019 *)
PROG
(PARI) my(t='t+O('t^30)); Vec((1+t)*(1-t^6)/(1-29*t+434*t^6-406*t^7)) \\ G. C. Greubel, Sep 07 2017
(Magma) R<t>:=PowerSeriesRing(Integers(), 30); Coefficients(R!( (1+t)*(1-t^6)/(1-29*t+434*t^6-406*t^7) )); // G. C. Greubel, Aug 10 2019
(SageMath)
def A164027_list(prec):
P.<t> = PowerSeriesRing(ZZ, prec)
return P((1+t)*(1-t^6)/(1-29*t+434*t^6-406*t^7)).list()
A164027_list(30) # G. C. Greubel, Aug 10 2019
(GAP) a:=[30, 870, 25230, 731670, 21218430, 615334035];; for n in [7..30] do a[n]:=28*(a[n-1] +a[n-2]+a[n-3]+a[n-4]+a[n-5]) -406*a[n-6]; od; Concatenation([1], a); # G. C. Greubel, Aug 10 2019
CROSSREFS
Sequence in context: A162833 A163208 A163552 * A164666 A164983 A165515
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved