What choice of such an $A$ minimises the number of integers $m\leq n$ not divisible by any $a\in A$? Is this minimised by letting $n\geq q_1>q_2>\cdots$ be the consecutive primes in decreasing order and choosing $A=\{q_1,\ldots,q_k\}$ where $k$ is maximal such that \[\sum_{i=1}^k\frac{1}{q_i}\leq C?\]