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Number of maximally clustered permutations in S_n; the maximally clustered permutations are those that avoid 3421, 4312 and 4321.

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1, 2, 6, 21, 78, 298, 1157, 4539, 17936, 71251, 284188, 1137076, 4561093, 18333337, 73816489, 297635750 (list; graph; listen)

	OFFSET	`1,2`
	REFERENCES	`Jozsef Losonczy, Maximally clustered elements and Schubert varieties, Preprint (2006), to appear in Annals of Combinatorics.`
	LINKS	`H. Denoncourt and B. Jones, The enumeration of maximally clustered permutations.`
	FORMULA	`G.f.: (2x^2) / (-1+4x-2x^2+sqrt(1-4x)).`
	EXAMPLE	`a(5)=78 because there are 78 permutations of size 5 that avoid 3421, 4312 and 4321.`
	CROSSREFS	`Cf. A108600.` `Adjacent sequences: A129772 A129773 A129774 this_sequence A129776 A129777 A129778` `Sequence in context: A063023 A124292 A129776 this_sequence A054515 A052300 A121941`
	KEYWORD	`nonn`
	AUTHOR	`Brant Jones (brant(AT)math.washington.edu), May 17 2007`

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Last modified May 15 13:16 EDT 2008. Contains 139641 sequences.