cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A162879 Number of reduced words of length n in Coxeter group on 42 generators S_i with relations (S_i)^2 = (S_i S_j)^3 = I.

Original entry on oeis.org

1, 42, 1722, 69741, 2824080, 114340800, 4629407580, 187434189600, 7588784431200, 307252630616400, 12439960566432000, 503665724648352000, 20392280251485912000, 825637071380896320000, 33428168171083640640000
Offset: 0

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Author

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

Keywords

Comments

The initial terms coincide with those of A170761, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.

Crossrefs

Programs

  • GAP
    a:=[42,1722,69741];; for n in [4..20] do a[n]:=40*a[n-1]+40*a[n-2] -820*a[n-3]; od; Concatenation([1],a); # Muniru A Asiru, Oct 24 2018
    
  • Magma
    I:=[1,42,1722,69741]; [n le 4 select I[n] else 40*Self(n-1) +40*Self(n-2)-820*Self(n-3): n in [1..20]]; // Vincenzo Librandi, Apr 14 2017
    
  • Magma
    R:=PowerSeriesRing(Integers(), 20); Coefficients(R!((t^3 +2*t^2+2*t+1)/(820*t^3-40*t^2-40*t+1))); // G. C. Greubel, Oct 24 2018
    
  • Maple
    seq(coeff(series((x^3+2*x^2+2*x+1)/(820*x^3-40*x^2-40*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)/(820*t^3-40*t^2-40*t+1), {t, 0, 20}], t] (* Wesley Ivan Hurt, Apr 12 2017 *)
    Join[{1}, LinearRecurrence[{40, 40, -820}, {42, 1722, 69741}, 20]] (* Vincenzo Librandi, Apr 14 2017 *)
    coxG[{3, 820, -40}] (* The coxG program is at A169452 *) (* G. C. Greubel, Apr 27 2019 *)
  • PARI
    my(t='t+O('t^20)); Vec((t^3+2*t^2+2*t+1)/(820*t^3-40*t^2-40*t+1)) \\ G. C. Greubel, Oct 24 2018
    
  • Sage
    ((1+x)*(1-x^3)/(1 -41*x +860*x^3 -820*x^4)).series(x, 20).coefficients(x, sparse=False) # G. C. Greubel, Apr 27 2019

Formula

G.f.: (t^3 + 2*t^2 + 2*t + 1)/(820*t^3 - 40*t^2 - 40*t + 1).
a(n) = 40*a(n-1) + 40*a(n-2) - 820*a(n-3), n > 0. - Muniru A Asiru, Oct 24 2018
G.f.: (1+x)*(1-x^3)/(1 - 41*x + 860*x^3 - 820*x^4). - G. C. Greubel, Apr 27 2019