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A214611
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Number of permutations of length n sortable by a pop stack followed by a queue and then by a stack.
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1
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1, 2, 6, 24, 120, 685, 4148, 25661, 159829, 997870, 6240672, 39111747, 245782289, 1549368610
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OFFSET
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1,2
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LINKS
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EXAMPLE
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There are only a(6)=685 permutations of length 6 that can be sorted by this machine; the machine can sort all shorter permutations.
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CROSSREFS
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KEYWORD
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nonn,hard,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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