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Inversions on Permutation ​

Pairs i < j with p(i) > p(j).

On Permutation

Called as CombinatorialStat(x, "Inversions"). The head's page has its examples.

Live

FindStat St000018

The number of inversions of a permutation.

ObjectValue
[]0
[1]0
[1,2]0
[2,1]1
[1,2,3]0
[1,3,2]1
[2,1,3]1
[2,3,1]2

Data from FindStat, the combinatorial statistic finder; the page at findstat.org/St000018 has the rest.