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A166557
Number of reduced words of length n in Coxeter group on 12 generators S_i with relations (S_i)^2 = (S_i S_j)^12 = I.
1
1, 12, 132, 1452, 15972, 175692, 1932612, 21258732, 233846052, 2572306572, 28295372292, 311249095212, 3423740047266, 37661140519200, 414272545703280, 4556998002648960, 50126978028180240, 551396758299441120, 6065364341177895600, 66719007751681327680
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A003954, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.
LINKS
Index entries for linear recurrences with constant coefficients, signature (10,10,10,10,10,10,10,10,10,10,10,-55).
FORMULA
G.f.: (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)/(55*t^12 - 10*t^11 - 10*t^10 - 10*t^9 - 10*t^8 - 10*t^7 - 10*t^6 - 10*t^5 - 10*t^4 - 10*t^3 - 10*t^2 - 10*t +1).
From G. C. Greubel, Dec 03 2024: (Start)
a(n) = 10*Sum_{j=1..11} a(n-j) - 55*a(n-12).
G.f.: (1+t)*(1 - t^12)/(1 - 11*t + 65*t^12 - 55*t^13). (End)
MATHEMATICA
CoefficientList[Series[(1+t)*(1-t^12)/(1-11*t+65*t^12-55*t^13), {t, 0, 50}], t]
(* G. C. Greubel, May 17 2016; Dec 03 2024 *)
coxG[{12, 55, -10}] (* The coxG program is at A169452 *) (* G. C. Greubel, Dec 03 2024 *)
PROG
(Magma)
R<x>:=PowerSeriesRing(Integers(), 40);
Coefficients(R!( (1+x)*(1-x^12)/(1-11*x+65*x^12-55*x^13) )); // ~~~
(SageMath)
def A166557_list(prec):
P.<x> = PowerSeriesRing(ZZ, prec)
return P( (1+x)*(1-x^12)/(1-11*x+65*x^12-55*x^13) ).list()
A166557_list(40) # G. C. Greubel, Dec 03 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved