A076906 Meandric numbers for a river (or directed line) crossing two perpendicular roads at n points, beginning in the (-,-) quadrant and ending in the (+,+) quadrant if n even, in the (+,-) quadrant if n odd.

0, 1, 2, 5, 12, 31, 82, 218, 612, 1673, 4892, 13672, 41192, 117194, 361302, 1042970, 3274712, 9567393, 30490688, 89984282, 290353456

Offset

0,3

Links

Table of n, a(n) for n=0..20.

Crossrefs

Cf. A005316, A076875 (undirected line), A076876, A076907 (end anywhere).

Sequence in context: A317098 A238427 A077556 * A097893 A093379 A271929

Adjacent sequences: A076903 A076904 A076905 * A076907 A076908 A076909

Keyword

nonn,more,nice

Author

N. J. A. Sloane and Jon Wild, Nov 26 2002

Extensions

a(7) corrected Aug 25 2003

a(7) corrected and a(8)-a(20) added by Robert Price, Jul 29 2012

Status

approved