A077055 - OEIS

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A077055

Call two meanders from A005316 equivalent if they differ by a reflection in the Y axis (if n even) or by reflections in the X or Y axes (if n odd). Sequence gives number of inequivalent meanders with n crossings.

1, 1, 1, 1, 2, 3, 8, 13, 42 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,5`
	FORMULA	`For n even a(n) = (A005316(n)+A005316(n/2))/2 (this is A078592).`
	EXAMPLE	`For n=7 the A005316(7) = 42 meanders with 7 crossings fall into 5 equivalence classes of size 2 and 8 of size 4, so a(7) = 5+8 = 13.`
	CROSSREFS	`Cf. A005316, A077460, A078592.` `Sequence in context: A151889 A129873 A025575 * A145929 A153865 A022951` `Adjacent sequences: A077052 A077053 A077054 * A077056 A077057 A077058`
	KEYWORD	`nonn,more,nice`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com) and Jon Wild (wild(AT)music.mcgill.ca), Nov 29 2002`

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Last modified February 14 18:33 EST 2012. Contains 205663 sequences.