Identifier
- St000866: Permutations ⟶ ℤ
Values
[1,2] => 0
[2,1] => 0
[1,2,3] => 0
[1,3,2] => 0
[2,1,3] => 1
[2,3,1] => 0
[3,1,2] => 2
[3,2,1] => 0
[1,2,3,4] => 0
[1,2,4,3] => 0
[1,3,2,4] => 1
[1,3,4,2] => 0
[1,4,2,3] => 2
[1,4,3,2] => 0
[2,1,3,4] => 1
[2,1,4,3] => 1
[2,3,1,4] => 2
[2,3,4,1] => 0
[2,4,1,3] => 3
[2,4,3,1] => 0
[3,1,2,4] => 2
[3,1,4,2] => 2
[3,2,1,4] => 2
[3,2,4,1] => 1
[3,4,1,2] => 4
[3,4,2,1] => 0
[4,1,2,3] => 3
[4,1,3,2] => 3
[4,2,1,3] => 3
[4,2,3,1] => 2
[4,3,1,2] => 4
[4,3,2,1] => 0
[1,2,3,4,5] => 0
[1,2,3,5,4] => 0
[1,2,4,3,5] => 1
[1,2,4,5,3] => 0
[1,2,5,3,4] => 2
[1,2,5,4,3] => 0
[1,3,2,4,5] => 1
[1,3,2,5,4] => 1
[1,3,4,2,5] => 2
[1,3,4,5,2] => 0
[1,3,5,2,4] => 3
[1,3,5,4,2] => 0
[1,4,2,3,5] => 2
[1,4,2,5,3] => 2
[1,4,3,2,5] => 2
[1,4,3,5,2] => 1
[1,4,5,2,3] => 4
[1,4,5,3,2] => 0
[1,5,2,3,4] => 3
[1,5,2,4,3] => 3
[1,5,3,2,4] => 3
[1,5,3,4,2] => 2
[1,5,4,2,3] => 4
[1,5,4,3,2] => 0
[2,1,3,4,5] => 1
[2,1,3,5,4] => 1
[2,1,4,3,5] => 2
[2,1,4,5,3] => 1
[2,1,5,3,4] => 3
[2,1,5,4,3] => 1
[2,3,1,4,5] => 2
[2,3,1,5,4] => 2
[2,3,4,1,5] => 3
[2,3,4,5,1] => 0
[2,3,5,1,4] => 4
[2,3,5,4,1] => 0
[2,4,1,3,5] => 3
[2,4,1,5,3] => 3
[2,4,3,1,5] => 3
[2,4,3,5,1] => 1
[2,4,5,1,3] => 5
[2,4,5,3,1] => 0
[2,5,1,3,4] => 4
[2,5,1,4,3] => 4
[2,5,3,1,4] => 4
[2,5,3,4,1] => 2
[2,5,4,1,3] => 5
[2,5,4,3,1] => 0
[3,1,2,4,5] => 2
[3,1,2,5,4] => 2
[3,1,4,2,5] => 3
[3,1,4,5,2] => 2
[3,1,5,2,4] => 4
[3,1,5,4,2] => 2
[3,2,1,4,5] => 2
[3,2,1,5,4] => 2
[3,2,4,1,5] => 4
[3,2,4,5,1] => 1
[3,2,5,1,4] => 5
[3,2,5,4,1] => 1
[3,4,1,2,5] => 4
[3,4,1,5,2] => 4
[3,4,2,1,5] => 3
[3,4,2,5,1] => 2
[3,4,5,1,2] => 6
[3,4,5,2,1] => 0
[3,5,1,2,4] => 5
[3,5,1,4,2] => 5
[3,5,2,1,4] => 4
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Description
The number of admissible inversions of a permutation in the sense of Shareshian-Wachs.
An admissible inversion of a permutation $\sigma$ is a pair $(\sigma_i,\sigma_j)$ such that
1. $i < j$ and $\sigma_i > \sigma_j$ and 2. either $\sigma_j < \sigma_{j+1}$ or there exists a $i < k < j$ with $\sigma_k < \sigma_j$.
This version was introduced by John Shareshian and Michelle L. Wachs in [1], for a closely related version, see St000463The number of admissible inversions of a permutation..
An admissible inversion of a permutation $\sigma$ is a pair $(\sigma_i,\sigma_j)$ such that
1. $i < j$ and $\sigma_i > \sigma_j$ and 2. either $\sigma_j < \sigma_{j+1}$ or there exists a $i < k < j$ with $\sigma_k < \sigma_j$.
This version was introduced by John Shareshian and Michelle L. Wachs in [1], for a closely related version, see St000463The number of admissible inversions of a permutation..
References
[1] Shareshian, J., Wachs, M. L. $q$-Eulerian polynomials: excedance number and major index MathSciNet:2300004
Code
def statistic(pi):
return sum( 1 for i,j in pi.inversions() if ( j < len(pi) and pi(j) < pi(j+1) ) or ( i+1 < j and pi(j) > min( pi(k) for k in range(i+1,j) ) ) )
Created
Jun 27, 2017 at 08:29 by Christian Stump
Updated
Jun 27, 2017 at 08:29 by Christian Stump
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