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A013927
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Begin with 2n cards in n piles of 2, the piles being {1,1},{2,2},{3,3},...,{n,n}. How many transpositions of adjacent (single) cards are needed to reverse the order of the piles?
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1
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OFFSET
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1,2
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REFERENCES
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Graham Brightwell, Michael Littman and Peter Winkler (pw(AT)research.bell-labs.com), unpublished.
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LINKS
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EXAMPLE
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a(3) = 5:
Start: {1,1} {2,2} {3,3}
Step 1: {2,1} {1,2} {3,3}
Step 2: {2,1} {3,2} {1,3}
Step 3: {2,3} {1,2} {1,3}
Step 4: {2,3} {3,2} {1,1}
Step 5: {3,3} {2,2} {1,1}
(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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