title: Project Euler problem number 4
body: <pre><code>n = 0
  for a in xrange(999, 100, -1):
      for b in xrange(a, 100, -1):
          x = a * b
          if x &gt; n:
              s = str(a * b)
              if s == s[::-1]:
                   n = a * b
  print n
  </code></pre>
  
  <p>I have a question about this solution to <a href="http://projecteuler.net/index.php?section=problems&amp;id=4" rel="nofollow">the problem</a>.
  I know it is right but I am wondering why in the <code>xrange(999,100,-1)</code> the <code>-1</code> is there
  For the a and b for loops. Please explain. I am new to this :)</p>