Identifier
- St000004: Permutations ⟶ ℤ
Values
[] => 0
[1] => 0
[1,2] => 0
[2,1] => 1
[1,2,3] => 0
[1,3,2] => 2
[2,1,3] => 1
[2,3,1] => 2
[3,1,2] => 1
[3,2,1] => 3
[1,2,3,4] => 0
[1,2,4,3] => 3
[1,3,2,4] => 2
[1,3,4,2] => 3
[1,4,2,3] => 2
[1,4,3,2] => 5
[2,1,3,4] => 1
[2,1,4,3] => 4
[2,3,1,4] => 2
[2,3,4,1] => 3
[2,4,1,3] => 2
[2,4,3,1] => 5
[3,1,2,4] => 1
[3,1,4,2] => 4
[3,2,1,4] => 3
[3,2,4,1] => 4
[3,4,1,2] => 2
[3,4,2,1] => 5
[4,1,2,3] => 1
[4,1,3,2] => 4
[4,2,1,3] => 3
[4,2,3,1] => 4
[4,3,1,2] => 3
[4,3,2,1] => 6
[1,2,3,4,5] => 0
[1,2,3,5,4] => 4
[1,2,4,3,5] => 3
[1,2,4,5,3] => 4
[1,2,5,3,4] => 3
[1,2,5,4,3] => 7
[1,3,2,4,5] => 2
[1,3,2,5,4] => 6
[1,3,4,2,5] => 3
[1,3,4,5,2] => 4
[1,3,5,2,4] => 3
[1,3,5,4,2] => 7
[1,4,2,3,5] => 2
[1,4,2,5,3] => 6
[1,4,3,2,5] => 5
[1,4,3,5,2] => 6
[1,4,5,2,3] => 3
[1,4,5,3,2] => 7
[1,5,2,3,4] => 2
[1,5,2,4,3] => 6
[1,5,3,2,4] => 5
[1,5,3,4,2] => 6
[1,5,4,2,3] => 5
[1,5,4,3,2] => 9
[2,1,3,4,5] => 1
[2,1,3,5,4] => 5
[2,1,4,3,5] => 4
[2,1,4,5,3] => 5
[2,1,5,3,4] => 4
[2,1,5,4,3] => 8
[2,3,1,4,5] => 2
[2,3,1,5,4] => 6
[2,3,4,1,5] => 3
[2,3,4,5,1] => 4
[2,3,5,1,4] => 3
[2,3,5,4,1] => 7
[2,4,1,3,5] => 2
[2,4,1,5,3] => 6
[2,4,3,1,5] => 5
[2,4,3,5,1] => 6
[2,4,5,1,3] => 3
[2,4,5,3,1] => 7
[2,5,1,3,4] => 2
[2,5,1,4,3] => 6
[2,5,3,1,4] => 5
[2,5,3,4,1] => 6
[2,5,4,1,3] => 5
[2,5,4,3,1] => 9
[3,1,2,4,5] => 1
[3,1,2,5,4] => 5
[3,1,4,2,5] => 4
[3,1,4,5,2] => 5
[3,1,5,2,4] => 4
[3,1,5,4,2] => 8
[3,2,1,4,5] => 3
[3,2,1,5,4] => 7
[3,2,4,1,5] => 4
[3,2,4,5,1] => 5
[3,2,5,1,4] => 4
[3,2,5,4,1] => 8
[3,4,1,2,5] => 2
[3,4,1,5,2] => 6
[3,4,2,1,5] => 5
[3,4,2,5,1] => 6
[3,4,5,1,2] => 3
[3,4,5,2,1] => 7
[3,5,1,2,4] => 2
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Description
The major index of a permutation.
This is the sum of the positions of its descents,
$$\operatorname{maj}(\sigma) = \sum_{\sigma(i) > \sigma(i+1)} i.$$
Its generating function is $[n]_q! = [1]_q \cdot [2]_q \dots [n]_q$ for $[k]_q = 1 + q + q^2 + \dots q^{k-1}$.
A statistic equidistributed with the major index is called Mahonian statistic.
This is the sum of the positions of its descents,
$$\operatorname{maj}(\sigma) = \sum_{\sigma(i) > \sigma(i+1)} i.$$
Its generating function is $[n]_q! = [1]_q \cdot [2]_q \dots [n]_q$ for $[k]_q = 1 + q + q^2 + \dots q^{k-1}$.
A statistic equidistributed with the major index is called Mahonian statistic.
References
[1] Foata, D. Distributions eulériennes et mahoniennes sur le groupe des permutations MathSciNet:0519777
[2] Triangle of Mahonian numbers T(n,k): coefficients in expansion of Product_i=0..n-1 (1 + x + ... + x^i), where k ranges from 0 to A000217(n-1). OEIS:A008302
[2] Triangle of Mahonian numbers T(n,k): coefficients in expansion of Product_i=0..n-1 (1 + x + ... + x^i), where k ranges from 0 to A000217(n-1). OEIS:A008302
Code
def statistic(x):
return x.major_index()
Created
Sep 15, 2011 at 15:51 by Chris Berg
Updated
Feb 07, 2020 at 09:49 by Christian Stump
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