A negative answer to the Erd\H{o}s-S\'ark\H{o}zy question
For a finite set $A$ of positive integers, let $H(A)$ be its set of subset sums, and let $g_3(n)$ be the least $N$ for which some $n$-element set $A\subseteq\{1,\ldots,N\}$ has $H(A)$ free of nonconstant three-term arithmetic progressions. Erd\H{o}s and S\'ark\H{o}zy asked whether $g_3(n)\gg 3^n$. We prove \[ \liminf_{...