

A144924


Number of partitiontype permutations in S_n.


0



1, 2, 4, 13, 36, 126, 428, 1681, 6820, 29233, 127865, 592604, 2829477, 14118079, 72122117, 380843081, 2056927326, 11444517369, 65234523659, 380644223976, 2272831229113, 13857568536672, 86164285623173, 546196787212398
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OFFSET

1,2


COMMENTS

These permutations satisfy the condition that their descent set corresponds with a composition which is weakly decreasing under the bijection between subsets of {1,2,...,n1} to strict compositions of n via {d_1<d_2<...<d_k} maps to (d_1,d_2d_1,...,d_kd_k1,nd_k)


REFERENCES

R. P. Stanley, Enumerative Combinatorics, Wadsworth, Vol. 1, 1986, Vol. 2, 1999; see especially Chapter 1.
R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999 (Chapter 7)


LINKS

Table of n, a(n) for n=1..24.


EXAMPLE

For n=3, the 4 partitiontype permutations are (1 2 3) (1 3 2) (2 3 1) (3 2 1).


CROSSREFS

Sequence in context: A148249 A148250 A148251 * A148252 A268698 A174604
Adjacent sequences: A144921 A144922 A144923 * A144925 A144926 A144927


KEYWORD

hard,nice,nonn


AUTHOR

Sara Billey, Sep 25 2008


STATUS

approved



