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A309331
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Expansion of (x+x^3+x^5)/(1-x-3*x^3-x^5).
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1
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0, 1, 1, 2, 5, 9, 16, 32, 61, 114, 219, 418, 792, 1510, 2878, 5473, 10421, 19847, 37776, 71917, 136931, 260680, 496278, 944847, 1798804, 3424569, 6519790, 12412480, 23631034, 44989208, 85651217, 163064109, 310444213, 591028898, 1125210433
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OFFSET
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0,4
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COMMENTS
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a(n) is the number of 231-avoiding permutations of length n that have order 1 or 3.
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LINKS
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FORMULA
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G.f.: (1-x+x^2)*(1+x+x^2)/(1-x-3*x^3-x^5).
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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