

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
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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 EastWest 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: A027057 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



