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A164633
Number of reduced words of length n in Coxeter group on 20 generators S_i with relations (S_i)^2 = (S_i S_j)^7 = I.
0
1, 20, 380, 7220, 137180, 2606420, 49521980, 940917430, 17877427560, 339671055240, 6453748749960, 122621201556840, 2329802360424360, 44266235934106440, 841058313382886670, 15980104736337918420
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^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(171*t^7 - 18*t^6 - 18*t^5 - 18*t^4 - 18*t^3 - 18*t^2 - 18*t + 1).
CROSSREFS
Sequence in context: A163124 A163454 A163969 * A164911 A165348 A165882
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved