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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

%I

%S 1,2,13,213,7584,454380,39665160,4775586480

%N 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.

%C 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,

%H <a href="/index/La#lacings">Index entries for sequences related to shoe lacings</a>

%e 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.

%Y Cf. A078698, A078700, A078675.

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

%K nonn

%O 1,2

%A _Hugo Pfoertner_, Dec 18 2002

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Last modified January 21 11:21 EST 2019. Contains 319354 sequences. (Running on oeis4.)