title: How to print a triangle of integers with number of lines specified by the user?
body: <p>I would like to further exercise myself on the use of ArrayLists and Nested Loops, so I thought of the following interesting problem.</p>
  
  <p>The number of lines is specialized by the user and something would come out like this:</p>
  
  <pre><code>Enter a number: 5
  1
  2      3
  4      5      6
  7      8      9      10
  11     12     13     14     15
  </code></pre>
  
  <p>Can anybody give me some advice for doing this question? Thanks in advance!</p>