[seqfan] perms and set partitions
Joerg Arndt
arndt at jjj.de
Mon Jun 8 04:00:16 CEST 2009
Let ne be the excedance of a permutation p
(i.e. number of positions j where p(j)>j).
Let nt be the (minimal) number of transpositions of p.
We have nt >= ne, set m:=nt-ne
Let A(n,m) be the number of length-n permutations
with m==nt-ne. We obtain the following triangle
n: A(n,0) A(n,1) A(n,2) etc.
1: 1,
2: 2, 0,
3: 5, 1, 0,
4: 15, 8, 1, 0,
5: 52, 51, 16, 1, 0,
6: 203, 312, 172, 32, 1, 0,
7: 877, 1926, 1611, 561, 64, 1, 0,
8: 4140, 12224, 14289, 7744, 1794, 128, 1, 0,
9: 21147, 80401, 124410, 95255, 35755, 5655, 256, 1, 0,
Leftmost column appears to be:
A000110 Bell or exponential numbers
Is there a combinatorial interpretation of this table?
More information about the SeqFan
mailing list