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.

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

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: A102585 A367828 A227746 * A259795 A365593 A069569

Adjacent sequences: A078699 A078700 A078701 * A078703 A078704 A078705

Keyword

nonn

Author

Hugo Pfoertner, Dec 18 2002

Status

approved