In this problem we will run a segmented sieve for [l,r]. In sieve we will maintain “number of divisor of $n$ which is smaller or equal than $\sqrt{n}$".

For each, $i\in [1,\sqrt{r}]$ we will increase number of divisor of each multiple of $i$ in range $[max(l,i^2),r]$.

After the sieve we will multiply $2$ with each number of divisor, because if $i$ is a divisor of $n$ such that $i\le \sqrt{n}$ , we will have another divisor $\frac{n}{i} \ge \sqrt{n}$. [if n is a square number , we will subtract $1$ also after multiplication].

Reference:⌗