A209621 Meandric numbers for a river crossing up to 9 parallel roads at n points.

1, 1, 2, 4, 10, 23, 63, 155, 448, 1152, 3451, 9156, 28155, 76491, 240015, 664363, 2118804, 5954414, 19246816, 54772539, 179063855, 515006165, 1700131496, 4934242781, 16427135058, 48050970367, 161163698861, 474656662565, 1602509174036, 4748224219223, 16125057102402

Offset

0,3

Comments

Number of ways that a river (or directed line) that starts in the South and flows East can cross up to 9 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..36

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: A208452 A208453 A209383 * A209622 A209626 A209656

Adjacent sequences: A209618 A209619 A209620 * A209622 A209623 A209624

Keyword

nonn

Author

Robert Price, May 07 2012

Extensions

a(21)-a(36) from Andrew Howroyd, Dec 06 2015

Status

approved