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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 Andrew Howroyd, Table of n, a(n) for n = 0..40 CROSSREFS Cf. A005316 (sequence for one road; extensive references and links). Cf. A076876 (sequence for two parallel roads). Cf. A204352, A208062, A208126, A208452, A208453, A209383, A209621, A209622, A209626, A209656, A209657, A209660, A209707, A210344, A210478, A210567, A210592 (sequences for 3 to 19 parallel roads). Cf. A206432 (sequence for unlimited number of parallel roads). Cf. A076875, A076906, A076907. Sequence in context: A333105 A148071 A000636 * A195980 A136753 A289666 Adjacent sequences: A204349 A204350 A204351 * A204353 A204354 A204355 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.)