title: Looping index number in descending order using mathimatical expression
body: <p>I have a button, when I click on it, my program shows number between 0 and n (excluding n itself) in ascending order. Example: if <code>n = 5</code> then when I press button it shows <code>0 1 2 3 4 0 1 2 3 4 0 ...</code> and so on.
  Mathematically I can write it like <code>(i+1) mod n</code>, where i previous number.
  Is there mathematical expression to show numbers in descending order?</p>
  
  <pre><code>Ex.: 0 4 3 2 1 0 4 3 2 1 ...
  </code></pre>