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Search: id:A111285
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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; listen)
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OFFSET
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1,2
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REFERENCES
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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
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a(n)=4a(n-1)-3a(n-2)+2a(n-3); n>=4.
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MATHEMATICA
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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
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Sequence in context: A156831 A027061 A083323 this_sequence A052991 A108627 A148475
Adjacent sequences: A111282 A111283 A111284 this_sequence A111286 A111287 A111288
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KEYWORD
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nonn
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AUTHOR
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Len Smiley ( smiley (at) math.uaa.alaska.edu ), Nov 01 2005
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Nov 04 2005
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