Identifier
- St001528: Permutations ⟶ ℤ
Values
[1] => 1
[1,2] => 1
[2,1] => 1
[1,2,3] => 1
[1,3,2] => 3
[2,1,3] => 3
[2,3,1] => 2
[3,1,2] => 2
[3,2,1] => 3
[1,2,3,4] => 1
[1,2,4,3] => 6
[1,3,2,4] => 6
[1,3,4,2] => 8
[1,4,2,3] => 8
[1,4,3,2] => 6
[2,1,3,4] => 6
[2,1,4,3] => 9
[2,3,1,4] => 8
[2,3,4,1] => 9
[2,4,1,3] => 9
[2,4,3,1] => 8
[3,1,2,4] => 8
[3,1,4,2] => 9
[3,2,1,4] => 6
[3,2,4,1] => 8
[3,4,1,2] => 9
[3,4,2,1] => 9
[4,1,2,3] => 9
[4,1,3,2] => 8
[4,2,1,3] => 8
[4,2,3,1] => 6
[4,3,1,2] => 9
[4,3,2,1] => 9
[1,2,3,4,5] => 1
[1,2,3,5,4] => 10
[1,2,4,3,5] => 10
[1,2,4,5,3] => 20
[1,2,5,3,4] => 20
[1,2,5,4,3] => 10
[1,3,2,4,5] => 10
[1,3,2,5,4] => 45
[1,3,4,2,5] => 20
[1,3,4,5,2] => 45
[1,3,5,2,4] => 45
[1,3,5,4,2] => 20
[1,4,2,3,5] => 20
[1,4,2,5,3] => 45
[1,4,3,2,5] => 10
[1,4,3,5,2] => 20
[1,4,5,2,3] => 45
[1,4,5,3,2] => 45
[1,5,2,3,4] => 45
[1,5,2,4,3] => 20
[1,5,3,2,4] => 20
[1,5,3,4,2] => 10
[1,5,4,2,3] => 45
[1,5,4,3,2] => 45
[2,1,3,4,5] => 10
[2,1,3,5,4] => 45
[2,1,4,3,5] => 45
[2,1,4,5,3] => 44
[2,1,5,3,4] => 44
[2,1,5,4,3] => 45
[2,3,1,4,5] => 20
[2,3,1,5,4] => 44
[2,3,4,1,5] => 45
[2,3,4,5,1] => 44
[2,3,5,1,4] => 44
[2,3,5,4,1] => 45
[2,4,1,3,5] => 45
[2,4,1,5,3] => 44
[2,4,3,1,5] => 20
[2,4,3,5,1] => 45
[2,4,5,1,3] => 44
[2,4,5,3,1] => 44
[2,5,1,3,4] => 44
[2,5,1,4,3] => 45
[2,5,3,1,4] => 45
[2,5,3,4,1] => 20
[2,5,4,1,3] => 44
[2,5,4,3,1] => 44
[3,1,2,4,5] => 20
[3,1,2,5,4] => 44
[3,1,4,2,5] => 45
[3,1,4,5,2] => 44
[3,1,5,2,4] => 44
[3,1,5,4,2] => 45
[3,2,1,4,5] => 10
[3,2,1,5,4] => 45
[3,2,4,1,5] => 20
[3,2,4,5,1] => 45
[3,2,5,1,4] => 45
[3,2,5,4,1] => 20
[3,4,1,2,5] => 45
[3,4,1,5,2] => 44
[3,4,2,1,5] => 45
[3,4,2,5,1] => 44
[3,4,5,1,2] => 44
[3,4,5,2,1] => 44
[3,5,1,2,4] => 44
[3,5,1,4,2] => 45
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Description
The number of permutations such that the product with the permutation has the same number of fixed points.
More formally, given a permutation $\pi$, this is the number of permutations $\sigma$ such that $\pi$ and $\pi\sigma$ have the same number of fixed points.
Note that the number of permutations $\sigma$ such that $\pi$ and $\pi\sigma$ have the same cycle type is the size of the conjugacy class of $\pi$, St000690The size of the conjugacy class of a permutation..
More formally, given a permutation $\pi$, this is the number of permutations $\sigma$ such that $\pi$ and $\pi\sigma$ have the same number of fixed points.
Note that the number of permutations $\sigma$ such that $\pi$ and $\pi\sigma$ have the same cycle type is the size of the conjugacy class of $\pi$, St000690The size of the conjugacy class of a permutation..
References
[1] balli Number of Permutations? MathOverflow:144899
Code
def statistic(pi):
m = pi.number_of_fixed_points()
return sum(1 for tau in Permutations(pi.size()) if (pi*tau).number_of_fixed_points() == m)
Created
Apr 09, 2020 at 18:37 by Martin Rubey
Updated
Apr 09, 2020 at 18:37 by Martin Rubey
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