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A165348
Number of reduced words of length n in Coxeter group on 20 generators S_i with relations (S_i)^2 = (S_i S_j)^9 = I.
0
1, 20, 380, 7220, 137180, 2606420, 49521980, 940917620, 17877434780, 339671260630, 6453753948360, 122621324950440, 2329805172758760, 44266298257724040, 841059666427601160, 15980133653210465640
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.
FORMULA
G.f. (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)/(171*t^9 - 18*t^8 - 18*t^7 - 18*t^6 - 18*t^5 - 18*t^4 - 18*t^3 -
18*t^2 - 18*t + 1)
MATHEMATICA
coxG[{9, 171, -18}] (* The coxG program is at A169452 *) (* Harvey P. Dale, May 06 2018 *)
CROSSREFS
Sequence in context: A163969 A164633 A164911 * A165882 A063815 A166414
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved