1-2001 witten on board
Source: VII May Olympiad (Olimpiada de Mayo) 2001 L2 P5
September 19, 2022
number theorycombinatoricsgame
Problem Statement
On the board are written the natural numbers from to inclusive. You have to delete some numbers so that among those that remain undeleted it is impossible to choose two different numbers such that the result of their multiplication is equal to one of the numbers that remain undeleted. What is the minimum number of numbers that must be deleted? For that amount, present an example showing which numbers are erased. Justify why, if fewer numbers are deleted, the desired property is not obtained.