A085919 Number of ways a loop can cross three roads meeting in a Y n times.

3, 0, 3, 1, 9, 6, 45, 42, 279, 320, 1977, 2610, 15306, 22404, 126300, 200158, 1093515, 1846314, 9830547, 17481864

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: A166445 A374139 A298082 * A352613 A105824 A171911

Adjacent sequences: A085916 A085917 A085918 * A085920 A085921 A085922

Keyword

nonn

Author

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

Status

approved