cp's OEIS Frontend

A168978 Number of reduced words of length n in Coxeter group on 13 generators S_i with relations (S_i)^2 = (S_i S_j)^23 = I.

%I A168978 #8 Nov 25 2016 10:22:21
%S A168978 1,13,156,1872,22464,269568,3234816,38817792,465813504,5589762048,
%T A168978 67077144576,804925734912,9659108818944,115909305827328,
%U A168978 1390911669927936,16690940039135232,200291280469622784
%N A168978 Number of reduced words of length n in Coxeter group on 13 generators S_i with relations (S_i)^2 = (S_i S_j)^23 = I.
%C A168978 The initial terms coincide with those of A170732, although the two sequences are eventually different.
%C A168978 First disagreement at index 23: a(23) = 7176798705861673428713394, A170732(23) = 7176798705861673428713472. - Klaus Brockhaus, Apr 19 2011
%C A168978 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168978 <a href="/index/Rec#order_23">Index entries for linear recurrences with constant coefficients</a>, signature (11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, -66).
%F A168978 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)/(66*t^23 - 11*t^22 - 11*t^21 - 11*t^20 - 11*t^19 - 11*t^18 - 11*t^17 - 11*t^16 - 11*t^15 - 11*t^14 - 11*t^13 - 11*t^12 - 11*t^11 - 11*t^10 - 11*t^9 - 11*t^8 - 11*t^7 - 11*t^6 - 11*t^5 - 11*t^4 - 11*t^3 - 11*t^2 - 11*t + 1).
%Y A168978 Cf. A170732 (G.f.: (1+x)/(1-12*x)).
%K A168978 nonn
%O A168978 0,2
%A A168978 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009