二項分布(binomial distribution)

$$B(n, p) = f_X(x) = \begin{cases} \displaystyle _nC_x\,p^x(1-p)^{n-x} & \quad x \in \left\{0,1,2, \dotsc ,n\right\}\\ \displaystyle　0 & \quad x \notin \left\{0,1,2, \dotsc ,n\right\} \end{cases} $$