Non-repetitive random number

Question

To generate Random numbers from 1- 20 I need to pick selective and it should not be repetitive.

How to do this in C#

Note I need to loop through as like this

Answer 1

Just like i did:

    list.Clear();
    int count = 0;
    
    while (count < 20)
    {            
        int x = Random.Range(1, 21);
        if (!list.Contains(x))
        {
            list.Add(x);
            count++;
        }
    }