  A set of integers greater than 1 is primitive if no element divides another.
Erd\H{o}s proved in 1935 that the sum of $1/(n \log n)$ for $n$ running over a
primitive set $A$ is universally bounded over all choices for $A$. In 1988 he
asked if this universal bound is attained by the set of prime numbers. We
answer the Erd\H{o}s question in the affirmative for 2-primitive sets. Here a
set is 2-primitive if no element divides the product of 2 other elements.
