Algo

import java.util.LinkedList;

public class Main
{

    public static void main(String[] args)
    {
        LinkedList<Integer> listOfFactor = new LinkedList<Integer>();
        long number = 600851475143L;
        for(int i = 3; i < number; i++)
        {
            if(number % i == 0 && isFactor(i))
                listOfFactor.add(i);
        }
        System.out.println("The most large factor is "+listOfFactor.getLast());
    }

    private static boolean isFactor(int numb)
    {
        if(numb == 1 || numb == 2)
            return true;

        for(int i = 1; i < numb; i++)
            if(numb % i == 0)
                return false;

        return true;
    }
}