$\displaystyle \int_0^x f(t) \mathop{}\!\mathrm{d} \displaystyle \int_0^x f(H_n = \sum_{i = 1}^{n} \frac{\sqrt{1 + \sqrt[p]{1 + a^2}}}{i}) \mathop{\displaystyle \int_0^x f(t) \mathop{}\!\mathrm{d} t}\!\mathrm{d} t$