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A165538 Number of permutations of length n which avoid the patterns 4312 and 3142. 0
1, 2, 6, 22, 88, 367, 1568, 6810, 29943, 132958, 595227, 2683373, 12170778, 55499358, 254297805, 1170248190, 5406570910, 25068420955, 116617923611, 544157590706, 2546278167018, 11945937322413, 56180864428301 (list; graph; refs; listen; history; internal format)
OFFSET

1,2

LINKS

M. Albert, M. Atkinson, and V. Vatter, Classes of permutations with infinitely many well-behaved simple permutations

Wikipedia, Permutation classes avoiding two patterns of length 4.

FORMULA

G.f. f satisfies (x^3-2*x^2+x)*f^4+(4*x^3-9*x^2+6*x-1)*f^3+(6*x^3-12*x^2+7*x-1)*f^2+(4*x^3-5*x^2+x)*f+x^3 = 0.

EXAMPLE

There are 22 permutations of length 4 which avoid these two patterns, so a(4)=22.

CROSSREFS

Sequence in context: A165536 A032351 A165537 * A165539 A109033 A049135

Adjacent sequences:  A165535 A165536 A165537 * A165539 A165540 A165541

KEYWORD

nonn

AUTHOR

Vince Vatter (vatter(AT)gmail.com), Sep 21 2009

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Last modified February 17 10:05 EST 2012. Contains 206009 sequences.