A165895 Number of reduced words of length n in Coxeter group on 22 generators S_i with relations (S_i)^2 = (S_i S_j)^10 = I.

1, 22, 462, 9702, 203742, 4278582, 89850222, 1886854662, 39623947902, 832102905942, 17474161024551, 366957381510720, 7706105011623480, 161828205241958640, 3398392310036308200, 71366238509821184160

Offset: 0

Author

John Cannon and N. J. A. Sloane, Dec 03 2009

Keywords

• nonn

Comments

The initial terms coincide with those of A170741, although the two sequences are eventually different.

Computed with MAGMA using commands similar to those used to compute A154638.

Links

• G. C. Greubel, Table of n, a(n) for n = 0..500
• Index entries for linear recurrences with constant coefficients, signature (20,20,20,20,20,20,20,20,20,-210).

Crossrefs

Cf. A154638, A170741.

Programs

GAP

a:=[22, 462, 9702, 203742, 4278582, 89850222, 1886854662, 39623947902, 832102905942, 17474161024551];; for n in [11..25] do a[n]:=20*Sum([1..9], j-> a[n-j]) -210*a[n-10]; od; Concatenation([1], a); # G. C. Greubel, Sep 25 2019

Magma

R:=PowerSeriesRing(Integers(), 20); Coefficients(R!( (1+t)*(1-t^10)/(1-21*t+230*t^10-210*t^11) )); // G. C. Greubel, Sep 25 2019

Maple

seq(coeff(series((1+t)*(1-t^10)/(1-21*t+230*t^10-210*t^11), t, n+1), t, n), n = 0..20); # G. C. Greubel, Sep 25 2019

Mathematica

CoefficientList[Series[(1+t)*(1-t^10)/(1-21*t+230*t^10-210*t^11), {t, 0, 25}], t] (* G. C. Greubel, Apr 17 2016 *)
coxG[{10, 210, -20}] (* The coxG program is at A169452 *) (* G. C. Greubel, Sep 25 2019 *)

PARI

my(t='t+O('t^20)); Vec((1+t)*(1-t^10)/(1-21*t+230*t^10-210*t^11)) \\ G. C. Greubel, Sep 25 2019

Sage

def A165895_list(prec):
    P. = PowerSeriesRing(ZZ, prec)
    return P((1+t)*(1-t^10)/(1-21*t+230*t^10-210*t^11)).list()
A165895_list(20) # G. C. Greubel, Sep 25 2019

Formula

G.f.: (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)/(210*t^10 - 20*t^9 - 20*t^8 - 20*t^7 - 20*t^6 - 20*t^5 - 20*t^4 - 20*t^3 - 20*t^2 - 20*t + 1).