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A111280
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Number of permutations avoiding the patterns {4231,4321,35142,45312,42513,45132,35412,45213,43512,456123,351624,451623,356124}; number of strong sorting class based on 4231.
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0
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1, 2, 6, 22, 113, 431, 1584, 5920, 22214, 83239, 311777, 1167902, 4375090, 16389450, 61395989, 229993639, 861572476, 3227511492, 12090486122, 45291815419, 169666341761, 635582108218, 2380935499534, 8919152662622, 33411776268873
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| M. Albert, R. Aldred, M. Atkinson, C Handley, D. Holton, D. McCaughan and H. van Ditmarsch, Sorting Classes, Elec. J. of Comb. 12 (2005)
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FORMULA
| a(n) = 4*a(n-1)-2*a(n-2)+4*a(n-3)-a(n-5).
G.f.: x*(1-2*x-2*x^3+29*x^4)/(1-4*x+2*x^2-4*x^3+x^5). [Colin Barker, Jan 16 2012]
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MATHEMATICA
| a[1] = 1; a[2] = 2; a[3] = 6; a[4] = 22; a[5] = 113; a[n_] := a[n] = 4a[n - 1] - 2a[n - 2] + 4a[n - 3] - a[n - 5]; Table[ a[n], {n, 25}] (* Robert G. Wilson v *)
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CROSSREFS
| Sequence in context: A064643 A129535 A014371 * A095817 A101042 A171339
Adjacent sequences: A111277 A111278 A111279 * A111281 A111282 A111283
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KEYWORD
| nonn,easy
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AUTHOR
| Len Smiley ( smiley (at) math.uaa.alaska.edu ), Nov 01 2005
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Nov 04 2005
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