In July 2020, Bloom and Sisask proved that any set such that \sum_{n \in A} \frac{1}{n} diverges must contain arithmetic progressions of length 3. This is the first non-trivial case of a
conjecture of
Erdős postulating that any such set must in fact contain arbitrarily long arithmetic progressions. In November 2020, in joint work with
James Maynard, he improved the best-known bound for
square-difference-free sets, showing that a set A \subset [N] with no square difference has size at most \frac{N}{(\log N)^{c\log \log\log N}} for some c>0. In December 2021, he proved that any set A \subset \mathbb{N} of positive upper density contains a finite S \subset A such that \sum_{n \in S} \frac{1}{n}=1. This answered a question of Erdős and Graham. == References ==