OPEN
Does there exist a maximal Sidon set $A\subset \{1,\ldots,N\}$ of size $O(N^{1/3})$?
A question of Erdős, Sárközy, and Sós
[ESS94]. It is easy to prove that the greedy construction of a maximal Sidon set in $\{1,\ldots,N\}$ has size $\gg N^{1/3}$. Ruzsa
[Ru98b] constructed a maximal Sidon set of size $\ll (N\log N)^{1/3}$.
See also [340].
