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A165215
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Number of reduced words of length n in Coxeter group on 8 generators S_i with relations (S_i)^2 = (S_i S_j)^9 = I.
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0
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1, 8, 56, 392, 2744, 19208, 134456, 941192, 6588344, 46118380, 322828464, 2259797904, 15818575920, 110729965584, 775109298096, 5425761859728, 37980310429488, 265862014886160, 1861032997362084, 13027223233652040
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OFFSET
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0,2
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COMMENTS
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The initial terms coincide with those of A003950, although the two sequences are eventually different.
Computed with MAGMA using commands similar to those used to compute A154638.
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LINKS
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Table of n, a(n) for n=0..19.
Index entries for linear recurrences with constant coefficients, signature (6, 6, 6, 6, 6, 6, 6, 6, -21).
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FORMULA
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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)/(21*t^9 - 6*t^8 - 6*t^7 - 6*t^6 - 6*t^5 - 6*t^4 - 6*t^3 - 6*t^2 - 6*t
+ 1)
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CROSSREFS
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Sequence in context: A163924 A164373 A164769 * A165786 A166366 A166538
Adjacent sequences: A165212 A165213 A165214 * A165216 A165217 A165218
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KEYWORD
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nonn
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AUTHOR
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John Cannon and N. J. A. Sloane, Dec 03 2009
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STATUS
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approved
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