Spring 2016, problem 14
A subset $A$ of the set $\{1,2,\dots,10000\}$ has the property that if $a,b$ are distinct elements of $A$, then $ab\not\in A$. What is the maximal number of elements in $A$?
A subset $A$ of the set $\{1,2,\dots,10000\}$ has the property that if $a,b$ are distinct elements of $A$, then $ab\not\in A$. What is the maximal number of elements in $A$?