login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A078105 Number of nonisomorphic ways a loop can cross three roads meeting in a Y n times (orbits under symmetry group of order 6). 5
1, 0, 1, 1, 2, 1, 8, 8, 48, 54, 331, 439, 2558, 3734, 21057, 33384, 182293, 307719, 1638465, 2913775, 15181584, 28194412, 144206012, 277887666, 1398566992 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,5
COMMENTS
There is no constraint on touching any particular sector.
The Mercedes-Benz problem: closed meanders crossing a Y.
LINKS
EXAMPLE
With three crossings the loop must cut each road exactly once, so a(3) = 1.
With 4 crossings the loop can cut one road 4 times (one possibility), or two roads twice each (one possibility), so a(4) = 2.
CROSSREFS
Cf. A078104 (total number of solutions), A077460 and A005315 (loop crossing one road).
Sequence in context: A086657 A188922 A036296 * A075513 A284211 A246403
KEYWORD
nonn,nice
AUTHOR
N. J. A. Sloane and Jon Wild, Dec 05 2002
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 22 11:56 EDT 2024. Contains 373570 sequences. (Running on oeis4.)