The number of negative entries in the character table of the Weyl group of a Cartan type.

The number of proper separations of a graph. A separation of a graph with vertex set $V$ is a set $\{A, B\}$ of subsets of $V$ such that $A\cup B = V$ and there is no edge between $A\setminus B$ and $B\setminus A$. A separation $\{A, B\}$ is proper $A\setminus B$ and $B\setminus A$ are non-empty. For example, the number of proper separations of the empty graph on $n$ vertices $\{1,\dots,n\}$ is the Stirling number of the second kind $S(n+1, 3)$, i.e., the number of set partitions of $\{0,1,\dots,n\}$ into three subsets, where the subset containing $0$ corresponds to $A \cap B$.

The number of forests contained in a graph. That is, for a graph $G = (V,E)$ with vertices $V$ and edges $E$, the number of subsets $E' \subseteq E$ for which the subgraph $(V,E')$ is acyclic. If $T_G(x,y)$ is the Tutte polynomial [2] of $G$, then the number of forests contained in $G$ is given by $T_G(2,1)$.

The sum of the entries in the column specified by the partition of the change of basis matrix from powersum symmetric functions to monomial symmetric functions. For example, $p_{22} = 2m_{22} + m_4$, so the statistic on the partition $22$ is 3.

The multiplicity of the irreducible representation corresponding to a partition in the relabelling action on rooted trees.

The number of connected components of the friends and strangers graph. Let $X$ and $Y$ be graphs with the same vertex set $\{1,\dots,n\}$. Then the friends-and-strangers graph has as vertex set the set of permutations $\mathfrak S_n$ and edges $\left(\sigma, (i, j)\circ\sigma\right)$ if $(i, j)$ is an edge of $X$ and $\left(\sigma(i), \sigma(j)\right)$ is an edge of $Y$. This statistic is the number of connected components of the friends and strangers graphs where $X=Y$. For example, if $X$ is a complete graph the statistic is $1$, if $X$ has no edges, the statistic is $n!$, and if $X$ is the path graph, the statistic is $$\sum_{k=0}^{\lfloor n/2\rfloor} (-1)^k (n-k)!\binom{n-k}{k},$$ see [thm. 2.2, 3].