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A111286
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Number of permutations avoiding the patterns {1342,1432,2341,2431,3142,3241,3412,3421,4132,4231,4312,4321}; number of strong sorting class based on 1342.
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5
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1, 2, 6, 12, 24, 48, 96, 192, 384, 768, 1536, 3072, 6144, 12288, 24576, 49152, 98304, 196608, 393216, 786432, 1572864, 3145728, 6291456, 12582912, 25165824, 50331648, 100663296, 201326592, 402653184, 805306368, 1610612736, 3221225472
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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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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index to sequences with linear recurrences with constant coefficients, signature (2).
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FORMULA
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a(n)=3*2^(n-2), n>=3.
a(n)=2*a(n-1) for n=3. G.f.: x*(1+2*x^2)/(1-2*x). [Colin Barker, Nov 29 2012]
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MATHEMATICA
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Table[If[n == 1, 1, If[n == 2, 2, 3*2^(n - 2)]], {n, 32}] (* Robert G. Wilson v *)
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CROSSREFS
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Cf. A003945, A007283, A042950, A098011, A110164 - differs from each by one initial term.
Sequence in context: A118224 A003680 A051487 * A058295 A132176 A197469
Adjacent sequences: A111283 A111284 A111285 * A111287 A111288 A111289
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KEYWORD
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nonn,easy
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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, Nov 04 2005
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STATUS
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approved
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