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A129775 Number of maximally clustered permutations in S_n; the maximally clustered permutations are those that avoid 3421, 4312 and 4321. +0
1
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.


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