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A335793
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Number of hare pop-stack sortable Cayley permutations.
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0
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OFFSET
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0,3
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COMMENTS
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Also, the set of Cayley permutations avoiding 231, 312, and 2121.
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LINKS
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FORMULA
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G.f.: (1 - 4*x + 4*x^2 - 2*x^3) / (1 - 5*x + 6*x^2 - 4*x^3).
a(n) = 5*a(n-1) - 6*a(n-2) + 4*a(n-3) for n>3.
(End)
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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