- FindStat

Identifier

St001960: Permutations ⟶ ℤ

Values

=>
                            
                            
                            
                            

                        [1,2]=>0
[2,1]=>0
[1,2,3]=>0
[1,3,2]=>1
[2,1,3]=>0
[2,3,1]=>0
[3,1,2]=>0
[3,2,1]=>1
[1,2,3,4]=>0
[1,2,4,3]=>1
[1,3,2,4]=>1
[1,3,4,2]=>1
[1,4,2,3]=>1
[1,4,3,2]=>2
[2,1,3,4]=>0
[2,1,4,3]=>1
[2,3,1,4]=>0
[2,3,4,1]=>0
[2,4,1,3]=>0
[2,4,3,1]=>1
[3,1,2,4]=>0
[3,1,4,2]=>1
[3,2,1,4]=>1
[3,2,4,1]=>1
[3,4,1,2]=>0
[3,4,2,1]=>1
[4,1,2,3]=>0
[4,1,3,2]=>1
[4,2,1,3]=>1
[4,2,3,1]=>1
[4,3,1,2]=>1
[4,3,2,1]=>2
[1,2,3,4,5]=>0
[1,2,3,5,4]=>1
[1,2,4,3,5]=>1
[1,2,4,5,3]=>1
[1,2,5,3,4]=>1
[1,2,5,4,3]=>2
[1,3,2,4,5]=>1
[1,3,2,5,4]=>2
[1,3,4,2,5]=>1
[1,3,4,5,2]=>1
[1,3,5,2,4]=>1
[1,3,5,4,2]=>2
[1,4,2,3,5]=>1
[1,4,2,5,3]=>2
[1,4,3,2,5]=>2
[1,4,3,5,2]=>2
[1,4,5,2,3]=>1
[1,4,5,3,2]=>2
[1,5,2,3,4]=>1
[1,5,2,4,3]=>2
[1,5,3,2,4]=>2
[1,5,3,4,2]=>2
[1,5,4,2,3]=>2
[1,5,4,3,2]=>3
[2,1,3,4,5]=>0
[2,1,3,5,4]=>1
[2,1,4,3,5]=>1
[2,1,4,5,3]=>1
[2,1,5,3,4]=>1
[2,1,5,4,3]=>2
[2,3,1,4,5]=>0
[2,3,1,5,4]=>1
[2,3,4,1,5]=>0
[2,3,4,5,1]=>0
[2,3,5,1,4]=>0
[2,3,5,4,1]=>1
[2,4,1,3,5]=>0
[2,4,1,5,3]=>1
[2,4,3,1,5]=>1
[2,4,3,5,1]=>1
[2,4,5,1,3]=>0
[2,4,5,3,1]=>1
[2,5,1,3,4]=>0
[2,5,1,4,3]=>1
[2,5,3,1,4]=>1
[2,5,3,4,1]=>1
[2,5,4,1,3]=>1
[2,5,4,3,1]=>2
[3,1,2,4,5]=>0
[3,1,2,5,4]=>1
[3,1,4,2,5]=>1
[3,1,4,5,2]=>1
[3,1,5,2,4]=>1
[3,1,5,4,2]=>2
[3,2,1,4,5]=>1
[3,2,1,5,4]=>2
[3,2,4,1,5]=>1
[3,2,4,5,1]=>1
[3,2,5,1,4]=>1
[3,2,5,4,1]=>2
[3,4,1,2,5]=>0
[3,4,1,5,2]=>1
[3,4,2,1,5]=>1
[3,4,2,5,1]=>1
[3,4,5,1,2]=>0
[3,4,5,2,1]=>1
[3,5,1,2,4]=>0
[3,5,1,4,2]=>1
[3,5,2,1,4]=>1
[3,5,2,4,1]=>1
[3,5,4,1,2]=>1
[3,5,4,2,1]=>2
[4,1,2,3,5]=>0
[4,1,2,5,3]=>1
[4,1,3,2,5]=>1
[4,1,3,5,2]=>1
[4,1,5,2,3]=>1
[4,1,5,3,2]=>2
[4,2,1,3,5]=>1
[4,2,1,5,3]=>2
[4,2,3,1,5]=>1
[4,2,3,5,1]=>1
[4,2,5,1,3]=>1
[4,2,5,3,1]=>2
[4,3,1,2,5]=>1
[4,3,1,5,2]=>2
[4,3,2,1,5]=>2
[4,3,2,5,1]=>2
[4,3,5,1,2]=>1
[4,3,5,2,1]=>2
[4,5,1,2,3]=>0
[4,5,1,3,2]=>1
[4,5,2,1,3]=>1
[4,5,2,3,1]=>1
[4,5,3,1,2]=>1
[4,5,3,2,1]=>2
[5,1,2,3,4]=>0
[5,1,2,4,3]=>1
[5,1,3,2,4]=>1
[5,1,3,4,2]=>1
[5,1,4,2,3]=>1
[5,1,4,3,2]=>2
[5,2,1,3,4]=>1
[5,2,1,4,3]=>2
[5,2,3,1,4]=>1
[5,2,3,4,1]=>1
[5,2,4,1,3]=>1
[5,2,4,3,1]=>2
[5,3,1,2,4]=>1
[5,3,1,4,2]=>2
[5,3,2,1,4]=>2
[5,3,2,4,1]=>2
[5,3,4,1,2]=>1
[5,3,4,2,1]=>2
[5,4,1,2,3]=>1
[5,4,1,3,2]=>2
[5,4,2,1,3]=>2
[5,4,2,3,1]=>2
[5,4,3,1,2]=>2
[5,4,3,2,1]=>3
                    

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Description

The number of descents of a permutation minus one if its first entry is not one.
This statistic appears in [1, Theorem 2.3] in a gamma-positivity result, see also [2].

References

[1] Athanasiadis, C. A. Gamma-positivity in combinatorics and geometry MathSciNet:3878174
[2] Shareshian, J., Wachs, M. L. Gamma-positivity of variations of Eulerian polynomials MathSciNet:4015851

Code

def statistic(pi):
    if pi(1) == 1:
        return pi.number_of_descents()
    else:
        return pi.number_of_descents()-1

Created

Jan 08, 2025 at 11:27 by Christian Stump

Updated

Jan 08, 2025 at 11:27 by Christian Stump