cp's OEIS Frontend

A168987 Number of reduced words of length n in Coxeter group on 22 generators S_i with relations (S_i)^2 = (S_i S_j)^23 = I.

%I A168987 #8 Nov 25 2016 10:25:00
%S A168987 1,22,462,9702,203742,4278582,89850222,1886854662,39623947902,
%T A168987 832102905942,17474161024782,366957381520422,7706105011928862,
%U A168987 161828205250506102,3398392310260628142,71366238515473190982
%N A168987 Number of reduced words of length n in Coxeter group on 22 generators S_i with relations (S_i)^2 = (S_i S_j)^23 = I.
%C A168987 The initial terms coincide with those of A170741, although the two sequences are eventually different.
%C A168987 First disagreement at index 23: a(23) = 2699275202494323924878079482271, A170741(23) = 2699275202494323924878079482502. - Klaus Brockhaus, Apr 19 2011
%C A168987 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168987 <a href="/index/Rec#order_23">Index entries for linear recurrences with constant coefficients</a>, signature (20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, -210).
%F A168987 G.f.: (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)/(210*t^23 - 20*t^22 - 20*t^21 - 20*t^20 - 20*t^19 - 20*t^18 - 20*t^17 - 20*t^16 - 20*t^15 - 20*t^14 - 20*t^13 - 20*t^12 - 20*t^11 - 20*t^10 - 20*t^9 - 20*t^8 - 20*t^7 - 20*t^6 - 20*t^5 - 20*t^4 - 20*t^3 - 20*t^2 - 20*t + 1).
%Y A168987 Cf. A170741 (G.f.: (1+x)/(1-21*x)).
%K A168987 nonn
%O A168987 0,2
%A A168987 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009