|
Search: id:A144924
|
|
|
| A144924 |
|
Number of partition-type permutations in S_n. |
|
+0
1
|
|
| 1, 2, 4, 13, 36, 126, 428, 1681, 6820, 29233, 127865, 592604, 2829477, 14118079, 72122117, 380843081, 2056927326, 11444517369, 65234523659, 380644223976, 2272831229113, 13857568536672, 86164285623173, 546196787212398
(list; graph; listen)
|
|
|
OFFSET
|
1,2
|
|
|
COMMENT
|
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,...,n-1} to strict compositions of n via {d_1<d_2<...<d_k} maps to (d_1,d_2-d_1,...,d_k-d_k-1,n-d_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)
|
|
EXAMPLE
|
For n=3, the 4 partition-type permutations are (1 2 3) (1 3 2) (2 3 1) (3 2 1).
|
|
CROSSREFS
|
Sequence in context: A148249 A148250 A148251 this_sequence A148252 A148253 A148254
Adjacent sequences: A144921 A144922 A144923 this_sequence A144925 A144926 A144927
|
|
KEYWORD
|
hard,nice,nonn
|
|
AUTHOR
|
Sara Billey (billey(AT)math.washington.edu), Sep 25 2008
|
|
|
Search completed in 0.002 seconds
|
