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A111285
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Number of permutations avoiding the patterns {2431,3421,4231,4321,24513,42513,34512,43512}; number of strong sorting class based on 2431.
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1
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1, 2, 6, 20, 66, 216, 706, 2308, 7546, 24672, 80666, 263740, 862306, 2819336, 9217906, 30138228, 98537866, 322172592, 1053353226, 3443970860, 11260168946, 36815469656, 120369313506, 393551182948, 1286727730586, 4206996000512
(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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LINKS
| Index entries for sequences related to linear recurrences with constant coefficients, signature (4,-3,2).
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FORMULA
| a(n) = 4a(n-1) - 3a(n-2) + 2a(n-3); n>=4.
G.f.: x*(1-2*x+x^2)/(1-4*x+3*x^2-2*x^3).
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MATHEMATICA
| a[1] = 1; a[2] = 2; a[3] = 6; a[n_] := a[n] = 4a[n - 1] - 3a[n - 2] + 2a[n - 3]; Table[a[n], {n, 26}] (* Robert G. Wilson v *)
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CROSSREFS
| Sequence in context: A027061 A083323 A174846 * A052991 A108627 A193234
Adjacent sequences: A111282 A111283 A111284 * A111286 A111287 A111288
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KEYWORD
| nonn
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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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