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A162920
Number of reduced words of length n in Coxeter group on 3 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.
0
1, 3, 6, 12, 21, 36, 63, 108, 186, 321, 552, 951, 1638, 2820, 4857, 8364, 14403, 24804, 42714, 73557, 126672, 218139, 375654, 646908, 1114029, 1918452, 3303735, 5689308, 9797466, 16872057, 29055096, 50035311, 86164998, 148383348
OFFSET
0,2
COMMENTS
The initial terms coincide with those of A003945, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.
FORMULA
G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(t^4 - t^3 - t^2 - t + 1)
CROSSREFS
Sequence in context: A234248 A294387 A128128 * A247662 A337462 A215005
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Dec 03 2009
STATUS
approved