cp's OEIS Frontend

A168913 Number of reduced words of length n in Coxeter group on 44 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.

%I A168913 #10 Aug 31 2020 15:03:10
%S A168913 1,44,1892,81356,3498308,150427244,6468371492,278139974156,
%T A168913 11960018888708,514280812214444,22114074925221092,950905221784506956,
%U A168913 40888924536733799108,1758223755079553361644,75603621468420794550692
%N A168913 Number of reduced words of length n in Coxeter group on 44 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.
%C A168913 The initial terms coincide with those of A170763, although the two sequences are eventually different.
%C A168913 First disagreement at index 21: a(21) = 20550471382205508235406493545735098, A170763(21) = 20550471382205508235406493545736044. - Klaus Brockhaus, Apr 08 2011
%C A168913 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168913 <a href="/index/Rec#order_21">Index entries for linear recurrences with constant coefficients</a>, signature (42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, 42, -903).
%F A168913 G.f.: (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)/(903*t^21 - 42*t^20 - 42*t^19 - 42*t^18 - 42*t^17 - 42*t^16 - 42*t^15 - 42*t^14 - 42*t^13 - 42*t^12 - 42*t^11 - 42*t^10 - 42*t^9 - 42*t^8 - 42*t^7 - 42*t^6 - 42*t^5 - 42*t^4 - 42*t^3 - 42*t^2 - 42*t + 1).
%t A168913 coxG[{21,903,-42}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, Aug 31 2020 *)
%Y A168913 Cf. A170763 (G.f.: (1+x)/(1-43*x)).
%K A168913 nonn
%O A168913 0,2
%A A168913 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009