Identifier
- St000213: Permutations ⟶ ℤ
Values
[1] => 1
[1,2] => 2
[2,1] => 1
[1,2,3] => 3
[1,3,2] => 2
[2,1,3] => 2
[2,3,1] => 2
[3,1,2] => 1
[3,2,1] => 2
[1,2,3,4] => 4
[1,2,4,3] => 3
[1,3,2,4] => 3
[1,3,4,2] => 3
[1,4,2,3] => 2
[1,4,3,2] => 3
[2,1,3,4] => 3
[2,1,4,3] => 2
[2,3,1,4] => 3
[2,3,4,1] => 3
[2,4,1,3] => 2
[2,4,3,1] => 3
[3,1,2,4] => 2
[3,1,4,2] => 2
[3,2,1,4] => 3
[3,2,4,1] => 3
[3,4,1,2] => 2
[3,4,2,1] => 2
[4,1,2,3] => 1
[4,1,3,2] => 2
[4,2,1,3] => 2
[4,2,3,1] => 3
[4,3,1,2] => 2
[4,3,2,1] => 2
[1,2,3,4,5] => 5
[1,2,3,5,4] => 4
[1,2,4,3,5] => 4
[1,2,4,5,3] => 4
[1,2,5,3,4] => 3
[1,2,5,4,3] => 4
[1,3,2,4,5] => 4
[1,3,2,5,4] => 3
[1,3,4,2,5] => 4
[1,3,4,5,2] => 4
[1,3,5,2,4] => 3
[1,3,5,4,2] => 4
[1,4,2,3,5] => 3
[1,4,2,5,3] => 3
[1,4,3,2,5] => 4
[1,4,3,5,2] => 4
[1,4,5,2,3] => 3
[1,4,5,3,2] => 3
[1,5,2,3,4] => 2
[1,5,2,4,3] => 3
[1,5,3,2,4] => 3
[1,5,3,4,2] => 4
[1,5,4,2,3] => 3
[1,5,4,3,2] => 3
[2,1,3,4,5] => 4
[2,1,3,5,4] => 3
[2,1,4,3,5] => 3
[2,1,4,5,3] => 3
[2,1,5,3,4] => 2
[2,1,5,4,3] => 3
[2,3,1,4,5] => 4
[2,3,1,5,4] => 3
[2,3,4,1,5] => 4
[2,3,4,5,1] => 4
[2,3,5,1,4] => 3
[2,3,5,4,1] => 4
[2,4,1,3,5] => 3
[2,4,1,5,3] => 3
[2,4,3,1,5] => 4
[2,4,3,5,1] => 4
[2,4,5,1,3] => 3
[2,4,5,3,1] => 3
[2,5,1,3,4] => 2
[2,5,1,4,3] => 3
[2,5,3,1,4] => 3
[2,5,3,4,1] => 4
[2,5,4,1,3] => 3
[2,5,4,3,1] => 3
[3,1,2,4,5] => 3
[3,1,2,5,4] => 2
[3,1,4,2,5] => 3
[3,1,4,5,2] => 3
[3,1,5,2,4] => 2
[3,1,5,4,2] => 3
[3,2,1,4,5] => 4
[3,2,1,5,4] => 3
[3,2,4,1,5] => 4
[3,2,4,5,1] => 4
[3,2,5,1,4] => 3
[3,2,5,4,1] => 4
[3,4,1,2,5] => 3
[3,4,1,5,2] => 3
[3,4,2,1,5] => 3
[3,4,2,5,1] => 3
[3,4,5,1,2] => 3
[3,4,5,2,1] => 3
[3,5,1,2,4] => 2
[3,5,1,4,2] => 3
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Description
The number of weak exceedances (also weak excedences) of a permutation.
This is defined as
$$\operatorname{wex}(\sigma)=\#\{i:\sigma(i) \geq i\}.$$
The number of weak exceedances is given by the number of exceedances (see St000155The number of exceedances (also excedences) of a permutation.) plus the number of fixed points (see St000022The number of fixed points of a permutation.) of $\sigma$.
This is defined as
$$\operatorname{wex}(\sigma)=\#\{i:\sigma(i) \geq i\}.$$
The number of weak exceedances is given by the number of exceedances (see St000155The number of exceedances (also excedences) of a permutation.) plus the number of fixed points (see St000022The number of fixed points of a permutation.) of $\sigma$.
References
Triangle of Eulerian numbers T(n,k) (n>=1, 1 <= k <= n) read by rows. OEIS:A008292
Code
def statistic(pi):
return len([1 for i in range(len(pi)) if pi[i] >= i+1])
Created
Aug 26, 2014 at 14:33 by Martin Rubey
Updated
Mar 28, 2015 at 23:10 by Martin Rubey
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