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A072503 Number of ways to lace a shoe with n eyelet pairs such that there is no direct "horizontal" connection between any adjacent eyelet pair. 0
3, 45, 1824, 109560, 9520560, 1145057760 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

The lacing must not have any "straight connections" between adjacent eyelet pairs (e.g. 2<->2*n-1, 3<->2*n-2, 4<->2*n-3,....). There are no symmetric solutions.

LINKS

Table of n, a(n) for n=3..8.

Hugo Pfoertner, FORTRAN program to count non-straight shoe lacings and results for N=3,4

Index entries for sequences related to shoe lacings

EXAMPLE

The 6 non-straight lacings for n=3 are: 124536, 135426, 142356, 145326, 153246, 154236. Not counting mirror images we get a(3)=3.

PROG

FORTRAN program available at link.

CROSSREFS

Cf. A078602, A078698, A078702, A002866.

Sequence in context: A079484 A012494 A012780 * A154242 A283698 A163002

Adjacent sequences:  A072500 A072501 A072502 * A072504 A072505 A072506

KEYWORD

nonn

AUTHOR

Hugo Pfoertner, Jan 27 2003

STATUS

approved

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