Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                
A163958
Number of reduced words of length n in Coxeter group on 13 generators S_i with relations (S_i)^2 = (S_i S_j)^6 = I.
1
1, 13, 156, 1872, 22464, 269568, 3234738, 38815920, 465779886, 5589224784, 67069091232, 804809820672, 9657486564726, 115887063443580, 1390611458122458, 16686937868633604, 200238458992414128
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A170732, 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)/(66*t^6 - 11*t^5 - 11*t^4 - 11*t^3 - 11*t^2 - 11*t + 1).
a(n) = -66*a(n-6) + 11*Sum_{k=1..5} a(n-k). - Wesley Ivan Hurt, May 11 2021
MAPLE
seq(coeff(series((1+t)*(1-t^6)/(1-12*t+77*t^6-66*t^7), t, n+1), t, n), n = 0 .. 30); # G. C. Greubel, Aug 11 2019
MATHEMATICA
CoefficientList[Series[(1+t)*(1-t^6)/(1-12*t+77*t^6-66*t^7), {t, 0, 30}], t] (* G. C. Greubel, Aug 13 2017 *)
coxG[{6, 66, -11}] (* The coxG program is at A169452 *) (* G. C. Greubel, Aug 11 2019 *)
PROG
(PARI) my(t='t+O('t^30)); Vec((1+t)*(1-t^6)/(1-12*t+77*t^6-66*t^7)) \\ G. C. Greubel, Aug 13 2017
(Magma) R<t>:=PowerSeriesRing(Integers(), 30); Coefficients(R!( (1+t)*(1-t^6)/(1-12*t+77*t^6-66*t^7) )); // G. C. Greubel, Aug 11 2019
(Sage)
def A163878_list(prec):
P.<t> = PowerSeriesRing(ZZ, prec)
return P((1+t)*(1-t^6)/(1-12*t+77*t^6-66*t^7)).list()
A163878_list(30) # G. C. Greubel, Aug 11 2019
(GAP) a:=[13, 156, 1872, 22464, 269568, 3234738];; for n in [7..30] do a[n]:=11*(a[n-1] +a[n-2]+a[n-3]+a[n-4]+a[n-5]) -66*a[n-6]; od; Concatenation([1], a); # G. C. Greubel, Aug 11 2019
CROSSREFS
Sequence in context: A097827 A163084 A163438 * A164610 A164815 A165269
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved