How to generate 1000 random numbers from 0 to 1000000 then insert it into 16 rows

I've got a question. I need to generate 1000 random numbers from 0 to 1000000. Then I need to put it into 16 rows and save it into a new file. That's the beginning of this code. I'm a beginner. Could you please advise? How can I write this to use it then to multithreaded merge sort?

import java.util.Random;
import java.util.ArrayList;
import java.util.Collections;

    public class list1 {

        public static void main(String[] args) {
            ArrayList <Integer> list = new ArrayList();
            for (int i = 1; i < 1000000; i++) {
                list.add(i);
            }
            Collections.shuffle(list);
            for (int i = 0; i < 1000; i++) {
                System.out.println(list.get(i));
            }
        }

    }