- FindStat

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Identifier

St000027: Dyck paths ⟶ ℤ

Values

[] => 0

[1,0] => 0

[1,0,1,0] => 2

[1,1,0,0] => 0

[1,0,1,0,1,0] => 6

[1,0,1,1,0,0] => 2

[1,1,0,0,1,0] => 4

[1,1,0,1,0,0] => 3

[1,1,1,0,0,0] => 0

[1,0,1,0,1,0,1,0] => 12

[1,0,1,0,1,1,0,0] => 6

[1,0,1,1,0,0,1,0] => 8

[1,0,1,1,0,1,0,0] => 7

[1,0,1,1,1,0,0,0] => 2

[1,1,0,0,1,0,1,0] => 10

[1,1,0,0,1,1,0,0] => 4

[1,1,0,1,0,0,1,0] => 9

[1,1,0,1,0,1,0,0] => 8

[1,1,0,1,1,0,0,0] => 3

[1,1,1,0,0,0,1,0] => 6

[1,1,1,0,0,1,0,0] => 5

[1,1,1,0,1,0,0,0] => 4

[1,1,1,1,0,0,0,0] => 0

[1,0,1,0,1,0,1,0,1,0] => 20

[1,0,1,0,1,0,1,1,0,0] => 12

[1,0,1,0,1,1,0,0,1,0] => 14

[1,0,1,0,1,1,0,1,0,0] => 13

[1,0,1,0,1,1,1,0,0,0] => 6

[1,0,1,1,0,0,1,0,1,0] => 16

[1,0,1,1,0,0,1,1,0,0] => 8

[1,0,1,1,0,1,0,0,1,0] => 15

[1,0,1,1,0,1,0,1,0,0] => 14

[1,0,1,1,0,1,1,0,0,0] => 7

[1,0,1,1,1,0,0,0,1,0] => 10

[1,0,1,1,1,0,0,1,0,0] => 9

[1,0,1,1,1,0,1,0,0,0] => 8

[1,0,1,1,1,1,0,0,0,0] => 2

[1,1,0,0,1,0,1,0,1,0] => 18

[1,1,0,0,1,0,1,1,0,0] => 10

[1,1,0,0,1,1,0,0,1,0] => 12

[1,1,0,0,1,1,0,1,0,0] => 11

[1,1,0,0,1,1,1,0,0,0] => 4

[1,1,0,1,0,0,1,0,1,0] => 17

[1,1,0,1,0,0,1,1,0,0] => 9

[1,1,0,1,0,1,0,0,1,0] => 16

[1,1,0,1,0,1,0,1,0,0] => 15

[1,1,0,1,0,1,1,0,0,0] => 8

[1,1,0,1,1,0,0,0,1,0] => 11

[1,1,0,1,1,0,0,1,0,0] => 10

[1,1,0,1,1,0,1,0,0,0] => 9

[1,1,0,1,1,1,0,0,0,0] => 3

[1,1,1,0,0,0,1,0,1,0] => 14

[1,1,1,0,0,0,1,1,0,0] => 6

[1,1,1,0,0,1,0,0,1,0] => 13

[1,1,1,0,0,1,0,1,0,0] => 12

[1,1,1,0,0,1,1,0,0,0] => 5

[1,1,1,0,1,0,0,0,1,0] => 12

[1,1,1,0,1,0,0,1,0,0] => 11

[1,1,1,0,1,0,1,0,0,0] => 10

[1,1,1,0,1,1,0,0,0,0] => 4

[1,1,1,1,0,0,0,0,1,0] => 8

[1,1,1,1,0,0,0,1,0,0] => 7

[1,1,1,1,0,0,1,0,0,0] => 6

[1,1,1,1,0,1,0,0,0,0] => 5

[1,1,1,1,1,0,0,0,0,0] => 0

[1,0,1,0,1,0,1,0,1,0,1,0] => 30

[1,0,1,0,1,0,1,0,1,1,0,0] => 20

[1,0,1,0,1,0,1,1,0,0,1,0] => 22

[1,0,1,0,1,0,1,1,0,1,0,0] => 21

[1,0,1,0,1,0,1,1,1,0,0,0] => 12

[1,0,1,0,1,1,0,0,1,0,1,0] => 24

[1,0,1,0,1,1,0,0,1,1,0,0] => 14

[1,0,1,0,1,1,0,1,0,0,1,0] => 23

[1,0,1,0,1,1,0,1,0,1,0,0] => 22

[1,0,1,0,1,1,0,1,1,0,0,0] => 13

[1,0,1,0,1,1,1,0,0,0,1,0] => 16

[1,0,1,0,1,1,1,0,0,1,0,0] => 15

[1,0,1,0,1,1,1,0,1,0,0,0] => 14

[1,0,1,0,1,1,1,1,0,0,0,0] => 6

[1,0,1,1,0,0,1,0,1,0,1,0] => 26

[1,0,1,1,0,0,1,0,1,1,0,0] => 16

[1,0,1,1,0,0,1,1,0,0,1,0] => 18

[1,0,1,1,0,0,1,1,0,1,0,0] => 17

[1,0,1,1,0,0,1,1,1,0,0,0] => 8

[1,0,1,1,0,1,0,0,1,0,1,0] => 25

[1,0,1,1,0,1,0,0,1,1,0,0] => 15

[1,0,1,1,0,1,0,1,0,0,1,0] => 24

[1,0,1,1,0,1,0,1,0,1,0,0] => 23

[1,0,1,1,0,1,0,1,1,0,0,0] => 14

[1,0,1,1,0,1,1,0,0,0,1,0] => 17

[1,0,1,1,0,1,1,0,0,1,0,0] => 16

[1,0,1,1,0,1,1,0,1,0,0,0] => 15

[1,0,1,1,0,1,1,1,0,0,0,0] => 7

[1,0,1,1,1,0,0,0,1,0,1,0] => 20

[1,0,1,1,1,0,0,0,1,1,0,0] => 10

[1,0,1,1,1,0,0,1,0,0,1,0] => 19

[1,0,1,1,1,0,0,1,0,1,0,0] => 18

[1,0,1,1,1,0,0,1,1,0,0,0] => 9

[1,0,1,1,1,0,1,0,0,0,1,0] => 18

[1,0,1,1,1,0,1,0,0,1,0,0] => 17

[1,0,1,1,1,0,1,0,1,0,0,0] => 16

>>> Load all 1627 entries. <<<

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Description

The major index of a Dyck path.
This is the sum over all $i+j$ for which $(i,j)$ is a valley of $D$.
The generating function of the major index yields MacMahon 's $q$-Catalan numbers
$$\sum_{D \in \mathfrak{D}_n} q^{\operatorname{maj}(D)} = \frac{1}{[n+1]_q}\begin{bmatrix} 2n \\ n \end{bmatrix}_q,$$
where $[k]_q := 1+q+\ldots+q^{k-1}$ is the usual $q$-extension of the integer $k$, $[k]_q!:= [1]_q[2]_q \cdots [k]_q$ is the $q$-factorial of $k$ and $\left[\begin{smallmatrix} k \\ l \end{smallmatrix}\right]_q:=[k]_q!/[l]_q![k-l]_q!$ is the $q$-binomial coefficient.
The major index was first studied by P.A.MacMahon in [1], where he proved this generating function identity.
There is a bijection $\psi$ between Dyck paths and noncrossing permutations which simultaneously sends the area of a Dyck path St000012The area of a Dyck path. to the number of inversions St000018The number of inversions of a permutation., and the major index of the Dyck path to $n(n-1)$ minus the sum of the major index and the major index of the inverse [2].
For the major index on other collections, see St000004The major index of a permutation. for permutations and St000290The major index of a binary word. for binary words.

References

[1] MacMahon, P. A. Combinatory analysis MathSciNet:0141605
[2] Stump, C. More bijective Catalan combinatorics on permutations and on signed permutations arXiv:0808.2822

Code

def statistic(x):
    return x.major_index()

Created

Jun 10, 2012 at 08:35 by Christian Stump

Updated

Feb 12, 2018 at 22:26 by Martin Rubey