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A125762
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Number of planar Langford sequences.
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2
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0, 0, 1, 0, 0, 0, 0, 4, 0, 0, 16, 40, 0, 0, 194, 274, 0, 0, 2384, 4719, 0, 0, 31856, 62124, 0, 0, 426502, 817717, 0, 0, 5724640, 10838471, 0, 0, 75178742, 142349245, 0, 0, 977964587, 1850941916, 0, 0
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OFFSET
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1,8
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COMMENTS
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Enumerates the Langford sequences (counted by A014552) that have the additional property that we can draw noncrossing lines to connect the two 1s, the two 2s, ..., the two ns. For example, the four solutions for n=8 are 8642752468357131, 8613175368425724, 5286235743681417, 7528623574368141.
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REFERENCES
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D. E. Knuth, TAOCP, Vol. 4, in preparation.
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LINKS
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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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