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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 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.)