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A072503
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Number of ways to lace a shoe with n eyelet pairs such that there is no direct "horizontal" connection between any adjacent eyelet pair.
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0
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OFFSET
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3,1
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COMMENTS
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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.
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LINKS
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EXAMPLE
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The 6 non-straight lacings for n=3 are: 124536, 135426, 142356, 145326, 153246, 154236. Not counting mirror images we get a(3)=3.
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PROG
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FORTRAN program available at link.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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