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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. 23
0, 1, 2, 5, 12, 31, 82, 218, 612, 1673, 4892, 13672, 41192, 117194, 361302, 1042970, 3274712, 9567393, 30490688, 89984282, 290353456 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 13 07:13 EST 2019. Contains 329085 sequences. (Running on oeis4.)