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A078702 Number of ways to lace a shoe that has n pairs of eyelets such that each eyelet has at least one direct connection to the opposite side. 4
1, 2, 13, 213, 7584, 454380, 39665160, 4775586480 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
The lace is "undirected": reversing the order of eyelets along the path does not count as a different solution. It must begin and end at the extreme pair of eyelets,
LINKS
EXAMPLE
a(3) = 13: 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 lacings are: 124356 154326 153426 142536 145236 135246 125346 124536 125436 152346 153246 152436 154236.
CROSSREFS
a(n) = ( A078698(n) + A078700(n) ) / 2
Sequence in context: A102585 A367828 A227746 * A259795 A365593 A069569
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Dec 18 2002
STATUS
approved

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Last modified May 18 15:59 EDT 2024. Contains 372664 sequences. (Running on oeis4.)