cp's OEIS Frontend

A168862 Number of reduced words of length n in Coxeter group on 41 generators S_i with relations (S_i)^2 = (S_i S_j)^20 = I.

%I A168862 #8 Nov 24 2016 18:40:19
%S A168862 1,41,1640,65600,2624000,104960000,4198400000,167936000000,
%T A168862 6717440000000,268697600000000,10747904000000000,429916160000000000,
%U A168862 17196646400000000000,687865856000000000000,27514634240000000000000
%N A168862 Number of reduced words of length n in Coxeter group on 41 generators S_i with relations (S_i)^2 = (S_i S_j)^20 = I.
%C A168862 The initial terms coincide with those of A170760, although the two sequences are eventually different.
%C A168862 First disagreement at index 20: a(20) = 112699941847039999999999999999180, A170760(20) = 112699941847040000000000000000000. - Klaus Brockhaus, Apr 04 2011
%C A168862 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168862 <a href="/index/Rec#order_20">Index entries for linear recurrences with constant coefficients</a>, signature (39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, 39, -780).
%F A168862 G.f.: (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)/(780*t^20 - 39*t^19 - 39*t^18 - 39*t^17 - 39*t^16 - 39*t^15 - 39*t^14 - 39*t^13 - 39*t^12 - 39*t^11 - 39*t^10 - 39*t^9 - 39*t^8 - 39*t^7 - 39*t^6 - 39*t^5 - 39*t^4 - 39*t^3 - 39*t^2 - 39*t + 1).
%Y A168862 Cf. A170760 (G.f.: (1+x)/(1-40*x)).
%K A168862 nonn
%O A168862 0,2
%A A168862 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009