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%I
%S 3,45,1824,109560,9520560,1145057760
%N Number of ways to lace a shoe with n eyelet pairs such that there is no direct "horizontal" connection between any adjacent eyelet pair.
%C 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.
%H Hugo Pfoertner, <a href="http://www.randomwalk.de/shoelace/nonstra.txt">FORTRAN program to count non-straight shoe lacings and results for N=3,4</a>
%H <a href="/index/La#lacings">Index entries for sequences related to shoe lacings</a>
%e The 6 non-straight lacings for n=3 are: 124536, 135426, 142356, 145326, 153246, 154236. Not counting mirror images we get a(3)=3.
%o FORTRAN program available at link.
%Y Cf. A078602, A078698, A078702, A002866.
%K nonn
%O 3,1
%A _Hugo Pfoertner_, Jan 27 2003
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