A099743 - OEIS

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A099743

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

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; refs; listen; history; internal format)

	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: A125903 A178321 A007232 * A102289 A041243 A056079` `Adjacent sequences: A099740 A099741 A099742 * A099744 A099745 A099746`
	KEYWORD	`nonn`
	AUTHOR	`Mike Zabrocki (zabrocki(AT)mathstat.yorku.ca), Nov 09 2004`

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Last modified February 17 16:49 EST 2012. Contains 206058 sequences.