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1, 4, 24, 336, 5520, 203040, 7025760, 510370560, 30163311360, 3577017024000, 319851801561600, 55850407258060800, 7021439018770176000, 1692163531361176473600, 284409062346887622144000, 90395009213694143422464000, 19571060809440210728706048000, 7929132907666579072319471616000
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OFFSET
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1,2
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COMMENTS
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Let p = (p1..pn) and q = (q1..qn) be two random permutations of (1..n); call the pair (p,q) balanced if the number of i with pi > qi is the same as the number of i with pi < qi. Then a(n) is the number of balanced pairs.
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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Jan Lakota, Oct 04 2011
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EXTENSIONS
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STATUS
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approved
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