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

0,3

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.

Sequence in context: A210478 A210567 A210592 * A124480 A337179 A130967

Adjacent sequences: A206429 A206430 A206431 * A206433 A206434 A206435

Keyword

nonn,nice

Author

Robert Price, May 07 2012

Extensions

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

Status

approved