

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




OFFSET

3,1


COMMENTS

The lacing must not have any "straight connections" between adjacent eyelet pairs (e.g. 2<>2*n1, 3<>2*n2, 4<>2*n3,....). There are no symmetric solutions.


LINKS

Table of n, a(n) for n=3..8.
Hugo Pfoertner, FORTRAN program to count nonstraight shoe lacings and results for N=3,4
Index entries for sequences related to shoe lacings


EXAMPLE

The 6 nonstraight 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 A331710 A283698
Adjacent sequences: A072500 A072501 A072502 * A072504 A072505 A072506


KEYWORD

nonn


AUTHOR

Hugo Pfoertner, Jan 27 2003


STATUS

approved



