Identifier
- St000625: Permutations ⟶ ℤ
Values
[1,2] => 2
[2,1] => 2
[1,2,3] => 3
[1,3,2] => 4
[2,1,3] => 3
[2,3,1] => 4
[3,1,2] => 3
[3,2,1] => 3
[1,2,3,4] => 4
[1,2,4,3] => 5
[1,3,2,4] => 5
[1,3,4,2] => 5
[1,4,2,3] => 5
[1,4,3,2] => 5
[2,1,3,4] => 4
[2,1,4,3] => 5
[2,3,1,4] => 5
[2,3,4,1] => 5
[2,4,1,3] => 5
[2,4,3,1] => 5
[3,1,2,4] => 4
[3,1,4,2] => 5
[3,2,1,4] => 4
[3,2,4,1] => 5
[3,4,1,2] => 5
[3,4,2,1] => 5
[4,1,2,3] => 4
[4,1,3,2] => 5
[4,2,1,3] => 4
[4,2,3,1] => 5
[4,3,1,2] => 4
[4,3,2,1] => 4
[1,2,3,4,5] => 5
[1,2,3,5,4] => 6
[1,2,4,3,5] => 6
[1,2,4,5,3] => 6
[1,2,5,3,4] => 7
[1,2,5,4,3] => 7
[1,3,2,4,5] => 6
[1,3,2,5,4] => 7
[1,3,4,2,5] => 6
[1,3,4,5,2] => 6
[1,3,5,2,4] => 7
[1,3,5,4,2] => 7
[1,4,2,3,5] => 6
[1,4,2,5,3] => 7
[1,4,3,2,5] => 6
[1,4,3,5,2] => 7
[1,4,5,2,3] => 7
[1,4,5,3,2] => 7
[1,5,2,3,4] => 6
[1,5,2,4,3] => 7
[1,5,3,2,4] => 6
[1,5,3,4,2] => 7
[1,5,4,2,3] => 6
[1,5,4,3,2] => 6
[2,1,3,4,5] => 5
[2,1,3,5,4] => 6
[2,1,4,3,5] => 6
[2,1,4,5,3] => 6
[2,1,5,3,4] => 7
[2,1,5,4,3] => 7
[2,3,1,4,5] => 6
[2,3,1,5,4] => 7
[2,3,4,1,5] => 6
[2,3,4,5,1] => 6
[2,3,5,1,4] => 7
[2,3,5,4,1] => 7
[2,4,1,3,5] => 6
[2,4,1,5,3] => 7
[2,4,3,1,5] => 6
[2,4,3,5,1] => 7
[2,4,5,1,3] => 7
[2,4,5,3,1] => 7
[2,5,1,3,4] => 6
[2,5,1,4,3] => 7
[2,5,3,1,4] => 6
[2,5,3,4,1] => 7
[2,5,4,1,3] => 6
[2,5,4,3,1] => 6
[3,1,2,4,5] => 5
[3,1,2,5,4] => 6
[3,1,4,2,5] => 6
[3,1,4,5,2] => 6
[3,1,5,2,4] => 7
[3,1,5,4,2] => 7
[3,2,1,4,5] => 5
[3,2,1,5,4] => 6
[3,2,4,1,5] => 6
[3,2,4,5,1] => 6
[3,2,5,1,4] => 7
[3,2,5,4,1] => 7
[3,4,1,2,5] => 6
[3,4,1,5,2] => 7
[3,4,2,1,5] => 6
[3,4,2,5,1] => 7
[3,4,5,1,2] => 7
[3,4,5,2,1] => 7
[3,5,1,2,4] => 6
[3,5,1,4,2] => 7
[3,5,2,1,4] => 6
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Description
The sum of the minimal distances to a greater element.
Set $\pi_0 = \pi_{n+1} = n+1$, then this statistic is
$$ \sum_{i=1}^n \min_d(\pi_{i-d}>\pi_i\text{ or }\pi_{i+d}>\pi_i) $$
This statistic appears in [1].
The generating function for the sequence of maximal values attained on $\mathfrak S_r$, $r\geq 0$ apparently coincides with [2], which satisfies the functional equation
$$ (x-1)^2 (x+1)^3 f(x^2) - (x-1)^2 (x+1) f(x) + x = 0. $$
Set $\pi_0 = \pi_{n+1} = n+1$, then this statistic is
$$ \sum_{i=1}^n \min_d(\pi_{i-d}>\pi_i\text{ or }\pi_{i+d}>\pi_i) $$
This statistic appears in [1].
The generating function for the sequence of maximal values attained on $\mathfrak S_r$, $r\geq 0$ apparently coincides with [2], which satisfies the functional equation
$$ (x-1)^2 (x+1)^3 f(x^2) - (x-1)^2 (x+1) f(x) + x = 0. $$
References
[1] newbie How to find a permutation of [n] so that $\sum \{\min (i-l[i],r[i]-i)\}$ is maximized? MathOverflow:251968
[2] Total number of 1's in binary expansions of 0, ..., n. OEIS:A000788
[2] Total number of 1's in binary expansions of 0, ..., n. OEIS:A000788
Code
def statistic(pi):
n = len(pi)
def closest_major(i):
ai = pi[i]
distance = 1
while True:
if (i-distance < 0 or pi[i-distance] >= ai or
i+distance >= n or pi[i+distance] >= ai):
return distance
distance += 1
return sum(closest_major(i) for i in range(n))
Created
Oct 15, 2016 at 21:57 by Martin Rubey
Updated
Oct 15, 2016 at 21:57 by Martin Rubey
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