cp's OEIS Frontend

A168907 Number of reduced words of length n in Coxeter group on 38 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.

%I A168907 #8 Nov 25 2016 09:42:13
%S A168907 1,38,1406,52022,1924814,71218118,2635070366,97497603542,
%T A168907 3607411331054,133474219248998,4938546112212926,182726206151878262,
%U A168907 6760869627619495694,250152176221921340678,9255630520211089605086
%N A168907 Number of reduced words of length n in Coxeter group on 38 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.
%C A168907 The initial terms coincide with those of A170757, although the two sequences are eventually different.
%C A168907 First disagreement at index 21: a(21) = 878654379333124031614077643897735, A170757(21) = 878654379333124031614077643898438. - Klaus Brockhaus, Apr 05 2011
%C A168907 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168907 <a href="/index/Rec#order_21">Index entries for linear recurrences with constant coefficients</a>, signature (36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, -666).
%F A168907 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)/(666*t^21 - 36*t^20 - 36*t^19 - 36*t^18 - 36*t^17 - 36*t^16 - 36*t^15 - 36*t^14 - 36*t^13 - 36*t^12 - 36*t^11 - 36*t^10 - 36*t^9 - 36*t^8 - 36*t^7 - 36*t^6 - 36*t^5 - 36*t^4 - 36*t^3 - 36*t^2 - 36*t + 1).
%Y A168907 Cf. A170757 (G.f.: (1+x)/(1-37*x)).
%K A168907 nonn
%O A168907 0,2
%A A168907 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009