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Search: id:A078104
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| A078104 |
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Number of ways a loop can cross three roads meeting in a Y n times. The loop must touch the South-West sector. |
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+0
5
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| 1, 0, 2, 1, 7, 6, 37, 42, 237, 320, 1715, 2610, 13478, 22404, 112480, 200158, 982561, 1846314, 8897089, 17481864
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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The Mercedes-Benz problem: closed meanders crossing a Y.
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LINKS
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Anonymous, Illustration for a(3) = 1
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EXAMPLE
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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 (giving A005315(2)*2 = 4 possibilities), or two roads twice each (3 ways), so a(4) = 7.
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CROSSREFS
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See A085919 for another version. Cf. A078105 (nonisomorphic solutions), A077460 and A005315 (loop crossing one road).
Cf. also A077550.
Sequence in context: A039814 A078301 A060583 this_sequence A072280 A086054 A011134
Adjacent sequences: A078101 A078102 A078103 this_sequence A078105 A078106 A078107
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KEYWORD
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nonn
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AUTHOR
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njas and Jon Wild (wild(AT)music.mcgill.ca), Dec 05 2002
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EXTENSIONS
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More terms added Aug 25, 2003
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