title: How to use BigInteger?
body: <p>I have this piece of code, which is not working:</p>
  
  <pre><code>BigInteger sum = BigInteger.valueOf(0);
  for(int i = 2; i &lt; 5000; i++) {
      if (isPrim(i)) {
          sum.add(BigInteger.valueOf(i));
      }
  }
  </code></pre>
  
  <p>The sum variable is always 0. What am I doing wrong?</p>