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A111286 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. 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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)

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Index to sequences with linear recurrences with constant coefficients, signature (2).

FORMULA

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]

G.f.: 2/G(0)+4*x, where G(k)= 1 + 1/(1 - x*(3*k+2)/(x*(3*k+5) + 1/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, May 25 2013

MATHEMATICA

Table[If[n == 1, 1, If[n == 2, 2, 3*2^(n - 2)]], {n, 32}] (* Robert G. Wilson v *)

CROSSREFS

Cf. A003945, A007283, A042950, A098011, A110164 - differs from each by one initial term.

Sequence in context: A227068 A003680 A051487 * A058295 A132176 A197469

Adjacent sequences:  A111283 A111284 A111285 * A111287 A111288 A111289

KEYWORD

nonn,easy

AUTHOR

Len Smiley ( smiley (at) math.uaa.alaska.edu ), Nov 01 2005

EXTENSIONS

More terms from Robert G. Wilson v, Nov 04 2005

STATUS

approved

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Last modified November 23 16:18 EST 2014. Contains 249851 sequences.