0,3

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

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]

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

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

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

Cf. A210668, A210669, A210671, A212417.

Sequence in context: A005387 A173469 A138549 * A144188 A157314 A159603

Adjacent sequences: A210664 A210665 A210666 * A210668 A210669 A210670

nonn

Tom Roby, May 08 2012

Definition improved by Tom Roby, May 15 2012

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

approved