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A165358
Number of reduced words of length n in Coxeter group on 21 generators S_i with relations (S_i)^2 = (S_i S_j)^9 = I.
0
1, 21, 420, 8400, 168000, 3360000, 67200000, 1344000000, 26880000000, 537599999790, 10751999991600, 215039999748210, 4300799993288400, 86015999832252000, 1720319995974720000, 34406399906088000000
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A170740, 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)/(190*t^9 - 19*t^8 - 19*t^7 - 19*t^6 - 19*t^5 - 19*t^4 - 19*t^3 -
19*t^2 - 19*t + 1)
MATHEMATICA
coxG[{9, 190, -19}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Aug 09 2020 *)
CROSSREFS
Sequence in context: A163977 A164634 A164954 * A165894 A166415 A166603
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved