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A085919 Number of ways a loop can cross three roads meeting in a Y n times. 1
3, 0, 3, 1, 9, 6, 45, 42, 279, 320, 1977, 2610, 15306, 22404, 126300, 200158, 1093515, 1846314, 9830547, 17481864 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

The Mercedes-Benz problem: closed meanders crossing a Y.

LINKS

Table of n, a(n) for n=0..19.

Anonymous, Illustration for a(3) = 1

EXAMPLE

With three crossings the loop must cut each road exactly once, so a(3) = 1.

CROSSREFS

Similar to A078104, but without the constraint of touching the (-, -) quadrant.

Sequence in context: A322575 A166445 A298082 * A105824 A171911 A180193

Adjacent sequences:  A085916 A085917 A085918 * A085920 A085921 A085922

KEYWORD

nonn

AUTHOR

N. J. A. Sloane and Jon Wild, Aug 25 2003

STATUS

approved

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Last modified April 17 11:08 EDT 2021. Contains 343064 sequences. (Running on oeis4.)