A206432 Meandric numbers for a river crossing any number of parallel roads at n points.

1, 1, 2, 4, 10, 23, 63, 155, 448, 1152, 3452, 9158, 28178, 76539, 240370, 665129, 2123439, 5964691, 19302316, 54898417, 179696559, 516468945, 1707136837, 4950706599, 16503343162, 48232630706, 161984048816, 476636485050, 1611287098347, 4769639932874, 16218699278307

Offset: 0

Author

Robert Price, May 07 2012

Keywords

• nonn
• nice

Comments

Number of ways that a river (or directed line) that starts in the South and flows East can cross any number of parallel East-West roads n times.

Of course, the number of roads crossed cannot be more than the number of crossings, n.

A file (28GB) listing all solutions through n=20 is available from the author.

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. A076875, A076906, A076907.

Extensions

a(21)-a(30) from Andrew Howroyd, Dec 07 2015