cp's OEIS Frontend

A169079 Number of reduced words of length n in Coxeter group on 18 generators S_i with relations (S_i)^2 = (S_i S_j)^25 = I.

%I A169079 #10 Nov 25 2016 11:57:31
%S A169079 1,18,306,5202,88434,1503378,25557426,434476242,7386096114,
%T A169079 125563633938,2134581776946,36287890208082,616894133537394,
%U A169079 10487200270135698,178282404592306866,3030800878069216722,51523614927176684274
%N A169079 Number of reduced words of length n in Coxeter group on 18 generators S_i with relations (S_i)^2 = (S_i S_j)^25 = I.
%C A169079 The initial terms coincide with those of A170737, although the two sequences are eventually different.
%C A169079 First disagreement at index 25: a(25) = 6110076083663014283583074108025, A170737(25) = 6110076083663014283583074108178. - Klaus Brockhaus, Apr 25 2011
%C A169079 Computed with MAGMA using commands similar to those used to compute A154638.
%H A169079 <a href="/index/Rec#order_25">Index entries for linear recurrences with constant coefficients</a>, signature (16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, -136).
%F A169079 G.f.: (t^25 + 2*t^24 + 2*t^23 + 2*t^22 + 2*t^21 + 2*t^20 + 2*t^19 + 2*t^18 + 2*t^17 + 2*t^16 + 2*t^15 + 2*t^14 + 2*t^13 + 2*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)/(136*t^25 - 16*t^24 - 16*t^23 - 16*t^22 - 16*t^21 - 16*t^20 - 16*t^19 - 16*t^18 - 16*t^17 - 16*t^16 - 16*t^15 - 16*t^14 - 16*t^13 - 16*t^12 - 16*t^11 - 16*t^10 - 16*t^9 - 16*t^8 - 16*t^7 - 16*t^6 - 16*t^5 - 16*t^4 - 16*t^3 - 16*t^2 - 16*t + 1).
%t A169079 With[{num=Total[2t^Range[24]]+t^25+1,den=Total[-16 t^Range[24]]+136t^25+ 1},CoefficientList[Series[num/den,{t,0,30}],t]] (* _Harvey P. Dale_, Jul 04 2013 *)
%Y A169079 Cf. A170737 (G.f.: (1+x)/(1-17*x)).
%K A169079 nonn
%O A169079 0,2
%A A169079 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009