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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 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 October 17 06:08 EDT 2019. Contains 328106 sequences. (Running on oeis4.)