

A163124


Number of reduced words of length n in Coxeter group on 20 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.


0



1, 20, 380, 7220, 136990, 2599200, 49316400, 935712000, 17753871510, 336855735180, 6391382632020, 121267853544780, 2300893742387430, 43656351283440360, 828320305398630840, 15716259104684097960
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OFFSET

0,2


COMMENTS

The initial terms coincide with those of A170739, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.


LINKS

Table of n, a(n) for n=0..15.
Index entries for linear recurrences with constant coefficients, signature (18, 18, 18, 171).


FORMULA

G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(171*t^4  18*t^3  18*t^2  18*t + 1)


MATHEMATICA

coxG[{4, 171, 18}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Dec 14 2015 *)


CROSSREFS

Sequence in context: A084329 A097832 A342886 * A163454 A163969 A164633
Adjacent sequences: A163121 A163122 A163123 * A163125 A163126 A163127


KEYWORD

nonn


AUTHOR

John Cannon and N. J. A. Sloane, Dec 03 2009


STATUS

approved



