\(f(x) = \frac{\binom{n_1}{x} \binom{n-n_1}{r-x}}{\binom{n}{r}}\) satisfies the properties of a probability function.
\(\displaystyle \mu = r \frac{n_1}{n}\)
\(\displaystyle \sigma^2 = r \frac{n_1}{n} \frac{n_2}{n} \frac{n-r}{n-1}\)
\(\displaystyle \gamma_1 = \frac{(n - 2 n_1)\sqrt{n-1}(n - 2r)}{r n_1 (n - n_1) \sqrt{n-r}(n-2)}\)
\(\gamma_2 = \) very complicated!