Problem:
For nine distinct positive integers we consider the polynomial .
One is to show that there exists an integer with the following property:
For all integers the number is divisible by a prime greater than 20.
Problem:
For nine distinct positive integers we consider the polynomial .
One is to show that there exists an integer with the following property:
For all integers the number is divisible by a prime greater than 20.
Solution:
According to the statement of the problem, we may assume and . Then . Let be chosen such that .
Claim: With a solution for has been found.
Proof: We assume that for none of the factors of has a prime factor greater than 20, and consider first . Since , there must then be at least one with (). Let the corresponding prime factor be . Thus is divisible by . Since , none of the other numbers () is divisible by , because otherwise would be divisible by . Thus . Now consider : there, because , we find at least one with as well as . Hence also has an that is maximal with respect to all factors. This holds correspondingly for the other factors .
Since, however, there are only 8 prime factors less than 20 for the 9 factors of the polynomial, a contradiction arises here by the pigeonhole principle. Therefore a further prime factor must occur, by which is divisible.