Given a finite group $G$ define $D(G)$ to be the number of divisors $r$ of $|G|$ for which there exists a subgroup of $G$ of order $r$.
Clearly $D(G) \leq d(|G|)$, where $d(n)$ denotes the number of divisors of $n$. We know that if $G$ is nilpotent or even supersolvable, more in general CLT ("Converse Lagrange Theorem", meaning that there exists a subgroup of size any given divisor) then $D(G) = d(|G|)$.
But do we have bounds in general?
Is it true that there exists a constant $C > 0$ such that $C \cdot D(G) \geq d(|G|)$ for any finite group $G$?
For example, what happens if we restrict our attention to symmetric/alternating groups?
This seems to be a hard problem, do you know if anyone has ever worked on this? Thank you for any contribution.