The 3-shifted major index of a permutation. This is given by the sum of all indices $i$ such that $\pi(i)-\pi(i+1) > 3$. Summing with [[St000494]] yields Rawlings' Mahonian statistic, see [1, p. 50].

The number of elements which do not have a complement in the lattice. A complement of an element $x$ in a lattice is an element $y$ such that the meet of $x$ and $y$ is the bottom element and their join is the top element.

The number of shortest chains of small intervals from the bottom to the top in a lattice. An interval $[a, b]$ in a lattice is small if $b$ is a join of elements covering $a$.

The size of the image of the pop stack sorting operator. The pop stack sorting operator is defined by $Pop_L^\downarrow(x) = x\wedge\bigwedge\{y\in L\mid y\lessdot x\}$. This statistic returns the size of $Pop_L^\downarrow(L)\}$.

The first Betti number of the order complex associated with the poset. The order complex of a poset is the simplicial complex whose faces are the chains of the poset. This statistic is the rank of the first homology group of the order complex.

Number of triples of incomparable elements in a finite poset. For a finite poset this is the number of 3-element sets $S \in \binom{P}{3}$ that are pairwise incomparable.