id:A099743 - OEIS Search Results

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Number of permutations with exactly 1 valley which avoid the pattern 1324.

+0
1

0, 0, 2, 15, 75, 313, 1179, 4161, 14051, 45993, 147195, 463345, 1440723, 4438905, 13582955, 41350977, 125404611, 379228489, 1144370139, 3447856017, 10375942835, 31198607385, 93749962827, 281584384225, 845476670115 (list; graph; listen)

	OFFSET	`1,3`
	FORMULA	`G.f.: (2-3x)x^3/((1-2x)^3(1-3*x)).`
	EXAMPLE	`a(3)=2 because 213 and 312 have exactly 1 valley and avoid 1324`
	CROSSREFS	`Cf. A000079.` `Sequence in context: A056037 A125903 A007232 this_sequence A102289 A041243 A056079` `Adjacent sequences: A099740 A099741 A099742 this_sequence A099744 A099745 A099746`
	KEYWORD	`nonn`
	AUTHOR	`Mike Zabrocki (zabrocki(AT)mathstat.yorku.ca), Nov 09 2004`

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Last modified December 18 21:37 EST 2009. Contains 171024 sequences.

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