Identifier
- St000458: Permutations ⟶ ℤ
Values
[1] => 1
[1,2] => 2
[2,1] => 2
[1,2,3] => 3
[1,3,2] => 3
[2,1,3] => 3
[2,3,1] => 3
[3,1,2] => 3
[3,2,1] => 3
[1,2,3,4] => 5
[1,2,4,3] => 5
[1,3,2,4] => 5
[1,3,4,2] => 3
[1,4,2,3] => 3
[1,4,3,2] => 3
[2,1,3,4] => 5
[2,1,4,3] => 5
[2,3,1,4] => 3
[2,3,4,1] => 3
[2,4,1,3] => 1
[2,4,3,1] => 3
[3,1,2,4] => 3
[3,1,4,2] => 1
[3,2,1,4] => 3
[3,2,4,1] => 3
[3,4,1,2] => 5
[3,4,2,1] => 5
[4,1,2,3] => 3
[4,1,3,2] => 3
[4,2,1,3] => 3
[4,2,3,1] => 5
[4,3,1,2] => 5
[4,3,2,1] => 5
[1,2,3,4,5] => 8
[1,2,3,5,4] => 8
[1,2,4,3,5] => 8
[1,2,4,5,3] => 6
[1,2,5,3,4] => 6
[1,2,5,4,3] => 6
[1,3,2,4,5] => 8
[1,3,2,5,4] => 8
[1,3,4,2,5] => 3
[1,3,4,5,2] => 3
[1,3,5,2,4] => 1
[1,3,5,4,2] => 3
[1,4,2,3,5] => 3
[1,4,2,5,3] => 1
[1,4,3,2,5] => 3
[1,4,3,5,2] => 3
[1,4,5,2,3] => 5
[1,4,5,3,2] => 5
[1,5,2,3,4] => 3
[1,5,2,4,3] => 3
[1,5,3,2,4] => 3
[1,5,3,4,2] => 5
[1,5,4,2,3] => 5
[1,5,4,3,2] => 5
[2,1,3,4,5] => 8
[2,1,3,5,4] => 8
[2,1,4,3,5] => 8
[2,1,4,5,3] => 6
[2,1,5,3,4] => 6
[2,1,5,4,3] => 6
[2,3,1,4,5] => 6
[2,3,1,5,4] => 6
[2,3,4,1,5] => 3
[2,3,4,5,1] => 5
[2,3,5,1,4] => 2
[2,3,5,4,1] => 5
[2,4,1,3,5] => 1
[2,4,1,5,3] => 1
[2,4,3,1,5] => 3
[2,4,3,5,1] => 5
[2,4,5,1,3] => 2
[2,4,5,3,1] => 3
[2,5,1,3,4] => 2
[2,5,1,4,3] => 2
[2,5,3,1,4] => 1
[2,5,3,4,1] => 3
[2,5,4,1,3] => 2
[2,5,4,3,1] => 3
[3,1,2,4,5] => 6
[3,1,2,5,4] => 6
[3,1,4,2,5] => 1
[3,1,4,5,2] => 2
[3,1,5,2,4] => 1
[3,1,5,4,2] => 2
[3,2,1,4,5] => 6
[3,2,1,5,4] => 6
[3,2,4,1,5] => 3
[3,2,4,5,1] => 5
[3,2,5,1,4] => 2
[3,2,5,4,1] => 5
[3,4,1,2,5] => 5
[3,4,1,5,2] => 2
[3,4,2,1,5] => 5
[3,4,2,5,1] => 3
[3,4,5,1,2] => 6
[3,4,5,2,1] => 6
[3,5,1,2,4] => 2
[3,5,1,4,2] => 1
>>> Load all 1201 entries. <<<
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Description
The number of permutations obtained by switching adjacencies or successions.
For a permutation $\pi$, this statistic is the size of its equivalence class of the equivalence relation generated by the interchange of any two adjacent elements $\pi_i$ and $\pi_{i+1}$ such that $|\pi_i - \pi_{i+1}| = 1$.
For a permutation $\pi$, this statistic is the size of its equivalence class of the equivalence relation generated by the interchange of any two adjacent elements $\pi_i$ and $\pi_{i+1}$ such that $|\pi_i - \pi_{i+1}| = 1$.
References
[1] Stanley, R. P. An equivalence relation on the symmetric group and multiplicity-free flag $h$-vectors MathSciNet:3029438 arXiv:1208.3540
[2] Amdeberhan, T. "flavored" equivalence classes of permutations MathOverflow:256673
[2] Amdeberhan, T. "flavored" equivalence classes of permutations MathOverflow:256673
Code
def statistic(pi):
def children(a):
for i in range(len(a)-1):
d = a[i] - a[i+1]
if d == 1 or d == -1:
yield Permutation(a[:i] + [a[i+1], a[i]] + a[i+2:])
return len([1 for pi in RecursivelyEnumeratedSet([Permutation(pi)], children)])
Created
Apr 05, 2016 at 17:34 by Jiang Zeng
Updated
May 10, 2019 at 17:36 by Henning Ulfarsson
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