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A165528
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Number of permutations of length n which avoid the patterns 1324 and 4231.
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0
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1, 2, 6, 22, 86, 336, 1282, 4758, 17234, 61242, 214594, 744594, 2566594, 8809442, 30157826, 103082050, 352045314, 1201795970, 4101913602, 13999868162, 47782800386, 163095158274, 556717514754, 1900427035650, 6487635578882
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| Kremer, Darla and Shiu, Wai Chee; Finite transition matrices for permutations avoiding pairs of length four patterns. Discrete Math. 268 (2003), 171-183. MR1983276 (2004b:05006). See Table 1.
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LINKS
| M. Albert, M. Atkinson, and V. Vatter, Counting 1324-, 4231-avoiding permutations
Wikipedia, Permutation classes avoiding two patterns of length 4
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FORMULA
| G.f.: (1-12*x+59*x^2-152*x^3+218*x^4-168*x^5+58*x^6-6*x^7)/(1-x)/(1-2*x)^4/(1-4*x+2* x^2)
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EXAMPLE
| There are 22 permutations of length 4 which avoid these two patterns, so a(4)=22.
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CROSSREFS
| Sequence in context: A165525 A165526 A165527 * A116709 A165529 A116710
Adjacent sequences: A165525 A165526 A165527 * A165529 A165530 A165531
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KEYWORD
| nonn,changed
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AUTHOR
| Vince Vatter (vatter(AT)gmail.com), Sep 21 2009
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