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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

Table of n, a(n) for n=1..8.

Index entries for sequences related to shoe lacings

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

Cf. A078698, A078700, A078675.

a(n) = ( A078698(n) + A078700(n) ) / 2

Sequence in context: A193550 A102585 A227746 * A259795 A069569 A255882

Adjacent sequences:  A078699 A078700 A078701 * A078703 A078704 A078705

KEYWORD

nonn

AUTHOR

Hugo Pfoertner, Dec 18 2002

STATUS

approved

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Last modified December 13 08:50 EST 2018. Contains 318082 sequences. (Running on oeis4.)