再生性
X 1 ∼ χ n 2 , X 2 ∼ χ m 2 ( n , m ∈ N ) ⟶ X 1 + X 2 ∼ χ n + m 2 {\displaystyle X_{1}\sim \chi _{n}^{2},X_{2}\sim \chi _{m}^{2}\ (n,m\in \mathbb {N} )\ \longrightarrow X_{1}+X_{2}\sim \chi _{n+m}^{2}}