id:A093346 - OEIS Search Results

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Array read by antidiagonals: T(r,n) = number of two-stack sortable r-permutations.

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1, 1, 2, 1, 3, 6, 1, 4, 15, 22, 1, 5, 28, 95, 91, 1, 6, 45, 252, 690, 408, 1, 7, 66, 525, 2618, 5481, 1938, 1, 8, 91, 946, 7095, 29848, 46376, 9614, 1, 9, 120, 1547, 15741, 105417, 363216, 411255, 49335, 1, 10, 153, 2360, 30576, 288288, 1673535 (list; table; graph; listen)

	OFFSET	`1,3`
	LINKS	`D. Xu, Generalizations of two-stack-sortable permutations, PhD thesis.`
	FORMULA	`T(r, n) = 2(r+1) * ((2r+1)n)!/[n!*(2rn+2)! ]`
	PROGRAM	`(PARI) T(r, n)=2(r+1)((2r+1)n)!/(n!(2r*n+2)!)`
	CROSSREFS	`Sequence in context: A046899 A035206 A115196 this_sequence A115597 A103371 A120257` `Adjacent sequences: A093343 A093344 A093345 this_sequence A093347 A093348 A093349`
	KEYWORD	`nonn,tabl`
	AUTHOR	`Ralf Stephan, Apr 26 2004`

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Last modified August 19 23:53 EDT 2008. Contains 142930 sequences.

AT&T Labs Research