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A163145
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Number of reduced words of length n in Coxeter group on 21 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.
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0
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1, 21, 420, 8400, 167790, 3351600, 66948210, 1337288400, 26712295890, 533577313500, 10658190898110, 212897044846500, 4252612111884990, 84945799915397400, 1696789816099808010, 33893325895893882600, 677018172425014524090, 13523417772619230573300
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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 A170740, 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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FORMULA
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G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(190*t^4 - 19*t^3 - 19*t^2 - 19*t + 1).
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MATHEMATICA
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PROG
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(PARI) Vec((t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(190*t^4 - 19*t^3 - 19*t^2 - 19*t + 1) + O(t^20)) \\ Jinyuan Wang, Mar 23 2020
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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