cp's OEIS Frontend

A168906 Number of reduced words of length n in Coxeter group on 37 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.

%I A168906 #10 Apr 04 2022 08:29:50
%S A168906 1,37,1332,47952,1726272,62145792,2237248512,80540946432,
%T A168906 2899474071552,104381066575872,3757718396731392,135277862282330112,
%U A168906 4870003042163884032,175320109517899825152,6311523942644393705472
%N A168906 Number of reduced words of length n in Coxeter group on 37 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.
%C A168906 The initial terms coincide with those of A170756, although the two sequences are eventually different.
%C A168906 First disagreement at index 21: a(21) = 494597297937218160510037301132646, A170756(21) = 494597297937218160510037301133312. - Klaus Brockhaus, Apr 05 2011
%C A168906 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168906 <a href="/index/Rec#order_21">Index entries for linear recurrences with constant coefficients</a>, signature (35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, 35, -630).
%F A168906 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)/(630*t^21 - 35*t^20 - 35*t^19 - 35*t^18 - 35*t^17 - 35*t^16 - 35*t^15 - 35*t^14 - 35*t^13 - 35*t^12 - 35*t^11 - 35*t^10 - 35*t^9 - 35*t^8 - 35*t^7 - 35*t^6 - 35*t^5 - 35*t^4 - 35*t^3 - 35*t^2 - 35*t + 1).
%t A168906 coxG[{21,630,-35}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, Apr 04 2022 *)
%Y A168906 Cf. A170756 (G.f.: (1+x)/(1-36*x)).
%K A168906 nonn
%O A168906 0,2
%A A168906 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009