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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
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
Sequence in context: A079484 A012494 A012780 * A154242 A331710 A283698
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Jan 27 2003
STATUS
approved

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Last modified May 25 16:17 EDT 2024. Contains 372801 sequences. (Running on oeis4.)