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A204352 Meandric numbers for a river crossing up to 3 parallel roads at n points. 19
1, 1, 2, 4, 9, 21, 52, 131, 345, 915, 2519, 6926, 19711, 55674, 162594, 468929, 1398129, 4100003, 12433282, 36960316, 113678461, 341785050, 1063890616, 3229522688, 10156518859, 31085477306, 98635931623, 304048850048, 972323924567, 3015979607106, 9711570455824 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
Number of ways that a river (or directed line) that starts in the South and flows East can cross 3 parallel East-West roads n times.
Sequence derived from list of solutions described in A206432.
LINKS
CROSSREFS
Cf. A005316 (sequence for one road; extensive references and links).
Cf. A076876 (sequence for two parallel roads).
Cf. A206432 (sequence for unlimited number of parallel roads).
Sequence in context: A333105 A148071 A000636 * A195980 A136753 A289666
KEYWORD
nonn
AUTHOR
Robert Price, May 07 2012
EXTENSIONS
a(21)-a(40) from Andrew Howroyd, Dec 07 2015
STATUS
approved

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Last modified July 19 22:34 EDT 2024. Contains 374441 sequences. (Running on oeis4.)