title: Find all the 4 digit vampire numbers
body: <p>I am solving a problem to find out all the 4 digit Vampire numbers.</p>
  
  <p>A <strong>Vampire Number</strong> v=x*y is defined as a number with 'n' even number of digits formed by multiplying a pair of 'n/2'-digit numbers (where the digits are taken from the original number in any order)x and y together. If v  is a vampire number, then x&amp;y and  are called its "fangs." </p>
  
  <p>Examples of vampire numbers are:</p>
  
  <pre><code>    1.    1260=21*60
      2.    1395=15*93
      3.    1530=30*51
  </code></pre>
  
  <p>I have tried the brute force algorithm to combine different digits of a given number and multiply them together . But this method is highly inefficient and takes up a lot of time.</p>
  
  <p>Is there a more efficient algorithmic solution to this problem?</p>