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A125762
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Number of planar Langford sequences.
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1
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,8
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COMMENTS
| 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
| D. E. Knuth, TAOCP, Vol. 4, in preparation.
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CROSSREFS
| Sequence in context: A028699 A019259 A019218 * A196302 A060784 A181204
Adjacent sequences: A125759 A125760 A125761 * A125763 A125764 A125765
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KEYWORD
| nonn
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AUTHOR
| D. E. Knuth, Feb 03 2007
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