cp's OEIS Frontend

A168892 Number of reduced words of length n in Coxeter group on 23 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.

%I A168892 #8 Nov 25 2016 09:37:36
%S A168892 1,23,506,11132,244904,5387888,118533536,2607737792,57370231424,
%T A168892 1262145091328,27767192009216,610878224202752,13439320932460544,
%U A168892 295665060514131968,6504631331310903296,143101889288839872512
%N A168892 Number of reduced words of length n in Coxeter group on 23 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.
%C A168892 The initial terms coincide with those of A170742, although the two sequences are eventually different.
%C A168892 First disagreement at index 21: a(21) = 16224878469787293016782798595, A170742(21) = 16224878469787293016782798848. - Klaus Brockhaus, Apr 05 2011
%C A168892 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168892 <a href="/index/Rec#order_21">Index entries for linear recurrences with constant coefficients</a>, signature (21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, -231).
%F A168892 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)/(231*t^21 - 21*t^20 - 21*t^19 - 21*t^18 - 21*t^17 - 21*t^16 - 21*t^15 - 21*t^14 - 21*t^13 - 21*t^12 - 21*t^11 - 21*t^10 - 21*t^9 - 21*t^8 - 21*t^7 - 21*t^6 - 21*t^5 - 21*t^4 - 21*t^3 - 21*t^2 - 21*t + 1).
%Y A168892 Cf. A170742 (G.f.: (1+x)/(1-22*x)).
%K A168892 nonn
%O A168892 0,2
%A A168892 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009