A076907 - OEIS

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A076907

Meandric numbers for a river crossing two perpendicular roads at n points, beginning in the (-,-) quadrant and ending in any quadrant.

2, 2, 6, 10, 32, 62, 210, 478 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,1`
	COMMENTS	`a(n) = number of ways that a directed curve (or arrow) can start in the (-,-) quadrant, cross the x and y axes at exactly n points and end in any quadrant.`
	FORMULA	`a(2n+1) = 2*A076906(2n+1).`
	CROSSREFS	`Cf. A005316, A076876, A076906, A076875 (undirected case).` `Cf. A077551 (cross x axis first).` `Sequence in context: A014113 A078008 A151575 * A153897 A103774 A036052` `Adjacent sequences: A076904 A076905 A076906 * A076908 A076909 A076910`
	KEYWORD	`nonn,more`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com) and Jon Wild (wild(AT)music.mcgill.ca), Nov 26 2002`
	EXTENSIONS	`a(6) and a(7) corrected Aug 25 2003`

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Last modified February 14 16:53 EST 2012. Contains 205635 sequences.