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A117514
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Number of ways of arranging 2n tokens in a row, with 2 copies of each token from 1 through n, such that the first token is a 1 and between every pair of tokens labeled i (i=1..n) there is exactly one taken labeled (i+1 mod n).
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3
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OFFSET
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1,3
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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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Nan Zang (nzang(AT)cs.ucsd.edu), Apr 28 2006
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STATUS
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approved
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