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A162921
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Number of reduced words of length n in Coxeter group on 4 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.
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0
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1, 4, 12, 36, 102, 288, 816, 2304, 6510, 18396, 51972, 146844, 414894, 1172232, 3312024, 9357768, 26439366, 74701620, 211061436, 596331540, 1684871094, 4760423280, 13450067520, 38001729168, 107369826654, 303361976844
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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 A003946, 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)/(3*t^4 - 2*t^3 - 2*t^2 - 2*t + 1)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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