Coupon collector's problem

赠券收集问题

调和数, Euler–Mascheroni constant

估算公式:$$\operatorname{E}(T) = n \cdot H_n = n \log n + \gamma n + \frac1{2} + o(1), \text{as} \ n \to \infty,$$ where $\gamma \approx 0.5772156649$ is the Euler–Mascheroni constant.