id:A111053 - OEIS Search Results

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Number of permutations which avoid the patterns 1324 and (2143 with Bruhat restriction {2<->3}). Also the number of permutations whose graphs are acyclic.

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1, 2, 6, 22, 89, 379, 1661, 7405, 33367, 151398, 690147, 3156112, 14465746, 66409493, 305232025, 1404129530 (list; graph; listen)

	OFFSET	`1,2`
	LINKS	`S. Butler, On permutations which are 1324 and {overline 2143} avoiding.` `M. Bousquet-Melou and S. Butler, Forest-like permutations`
	FORMULA	`G.f.: ((1-X)(1-4X-2XX)-(1-5X)sqrt(1-4X))/2/(1-5X+2*X^2-X^3. - Ralf Stephan, May 09 2007`
	CROSSREFS	`Sequence in context: A049137 A096267 A107944 this_sequence A049123 A049136 A049126` `Adjacent sequences: A111050 A111051 A111052 this_sequence A111054 A111055 A111056`
	KEYWORD	`nonn`
	AUTHOR	`Steven K. Butler (sbutler(AT)math.ucsd.edu), Oct 06 2005`

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Last modified July 26 23:19 EDT 2008. Contains 142293 sequences.

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