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A162882
Number of reduced words of length n in Coxeter group on 44 generators S_i with relations (S_i)^2 = (S_i S_j)^3 = I.
1
1, 44, 1892, 80410, 3416952, 145180728, 6168492330, 262088760780, 11135706433236, 473137249574682, 20102798001348216, 854133737629549608, 36290691560131770762, 1541929835910758016492, 65513979388697887768644
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A170763, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.
FORMULA
G.f.: (t^3 + 2*t^2 + 2*t + 1)/(903*t^3 - 42*t^2 - 42*t + 1).
a(n) = 42*a(n-1) + 42*a(n-2) - 903*a(n-3), n > 0. - Muniru A Asiru, Oct 24 2018
G.f.: (1+x)*(1-x^3)/(1 - 43*x + 945*x^3 - 903*x^4). - G. C. Greubel, Apr 27 2019
MAPLE
seq(coeff(series((x^3+2*x^2+2*x+1)/(903*x^3-42*x^2-42*x+1), x, n+1), x, n), n = 0 .. 20); # Muniru A Asiru, Oct 24 2018
MATHEMATICA
CoefficientList[Series[(t^3+2*t^2+2*t+1)/(903*t^3-42*t^2-42*t+1), {t, 0, 20}], t] (* G. C. Greubel, Oct 24 2018 *)
coxG[{3, 903, -42}] (* The coxG program is at A169452 *) (* G. C. Greubel, Apr 27 2019 *)
PROG
(PARI) my(t='t+O('t^20)); Vec((t^3+2*t^2+2*t+1)/(903*t^3-42*t^2-42*t+1)) \\ G. C. Greubel, Oct 24 2018
(Magma) R<t>:=PowerSeriesRing(Integers(), 20); Coefficients(R!((t^3 + 2*t^2+2*t+1)/(903*t^3-42*t^2-42*t+1))); // G. C. Greubel, Oct 24 2018
(GAP) a:=[44, 1892, 80410];; for n in [4..20] do a[n]:=42*a[n-1]+42*a[n-2] -903*a[n-3]; od; Concatenation([1], a); # Muniru A Asiru, Oct 24 2018
(Sage) ((1+x)*(1-x^3)/(1 -43*x +945*x^3 -903*x^4)).series(x, 20).coefficients(x, sparse=False) # G. C. Greubel, Apr 27 2019
CROSSREFS
Sequence in context: A223049 A278793 A004295 * A163230 A163748 A164277
KEYWORD
nonn,easy
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved