A210668 - OEIS

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A210668

Number of equivalence classes of S_n under transformations of positionally adjacent elements of the form abc <--> cba where a<b<c.

1, 1, 2, 5, 16, 60, 260, 1260, 6744, 39303

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OFFSET

0,3

LINKS

Table of n, a(n) for n=0..9.

Steven Linton, James Propp, Tom Roby, and Julian West, Equivalence classes of permutations under various relations generated by constrained transpositions, 2011 arXiv:1111.3920 [math.CO], J. Int. Seq. 15 (2012) #12.9.1

EXAMPLE

From Alois P. Heinz, May 16 2012: (Start)

a(3) = 5: {123, 321}, {132}, {213}, {231}, {312}.

a(4) = 16: {1234, 1432, 3214}, {1243, 4213}, {1324}, {1342, 4312}, {1423}, {2134, 2431}, {2143}, {2314}, {2341, 4123, 4321}, {2413}, {3124, 3421}, {3142}, {3241}, {3412}, {4132}, {4231}. (End)

CROSSREFS

Cf. A210667, A210669, A210671, A212417.

Sequence in context: A374543 A000764 A205486 * A279564 A005036 A012051

Adjacent sequences: A210665 A210666 A210667 * A210669 A210670 A210671

KEYWORD

nonn

AUTHOR

Tom Roby, May 08 2012

EXTENSIONS

Definition improved by Tom Roby, May 15 2012

a(0)-a(2), a(9) from Alois P. Heinz, May 16 2012

STATUS

approved