OPEN
Let $A\subseteq \mathbb{N}$ be such that
\[\lvert A\cap [1,2x]\rvert -\lvert A\cap [1,x]\rvert \to \infty\textrm{ as }x\to \infty\]
and
\[\sum_{n\in A} \{ \theta n\}=\infty\]
for every $\theta\in (0,1)$, where $\{x\}$ is the distance of $x$ from the nearest integer. Then every sufficiently large integer is the sum of distinct elements of $A$.
Cassels
[Ca60] proved this under the alternative hypotheses
\[\lvert A\cap [1,2x]\rvert -\lvert A\cap [1,x]\rvert\gg \log\log x\]
and
\[\sum_{n\in A} \{ \theta n\}^2=\infty\]
for every $\theta\in (0,1)$.
