Almost all primes have a multiple of small Hamming weight
  Recent results of Bourgain and Shparlinski imply that for almost all primes $p$ there is a multiple $mp$ that can be written in binary as $mp= 1+2^{m_1}+ \cdots +2^{m_k}, \quad 1\leq m_1 < \cdots < m_k,$ with $k=66$ or $k=16$, respectively. We show that $k=6$ (corresponding to Hamming weight $7$) suffices.   We also prove there are infinitely many primes $p$ with a multiplicative subgroup $A=<g>\subset \mathbb{F}_p^*$, for some   $g \in \{2,3,5\}$, of size $|A|\gg p/(\log p)^3$, where the sum-product set $A\cdot A+ A\cdot A$ does not cover $\mathbb{F}_p$ completely. 
Christian Elsholtz
math.NT math.CO