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A078676
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Number of symmetric ways to lace a shoe that has n pairs of eyelets.
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3
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OFFSET
| 1,2
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COMMENTS
| The lace must pass through each eyelet exactly once, must begin and end at the extreme pair of eyelets and cannot pass in order though three adjacent eyelets that are in a line.
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LINKS
| Index entries for sequences related to shoe lacings
N. J. A. Sloane, FORTRAN program
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EXAMPLE
| a(3) = 7: label the eyelets 1,2,3 from front to back on the left side then 4,5,6 from back to front on the right side. The symmetric lacings are: 124356 154326 153426 142536 145236 132546 135246.
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CROSSREFS
| Cf. A078602 for directed solutions, A078675 for undirected solutions.
Sequence in context: A050631 A146759 A144059 * A086331 A121418 A014501
Adjacent sequences: A078673 A078674 A078675 * A078677 A078678 A078679
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Dec 11 2002
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EXTENSIONS
| a(7) and a(8) from Hugo Pfoertner (hugo(AT)pfoertner.org), Jan 22 2005
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