title: Binary numbers of N digits
body: <p>for generating binary numbers in <code>n</code> digit<br>
  i did this to get upto 16 binary numbers.  </p>
  
  <pre><code>n = 6                       # for 6 digits
  for i in xrange(16):
      b = bin(i)[2:]
      l = len(b)
      b = str(0) * (n - l) + b
      print b
  </code></pre>
  
  <p>it results like this</p>
  
  <pre><code>000000
  000001
  000010
  000011
  000100
  000101
  000110
  000111
  001000
  001001
  001010
  001011
  001100
  001101
  001110
  001111
  </code></pre>
  
  <p>but what i want is to get these values without adding a series of <code>0s</code> in prefix.<br>
  can anyone help me for this.<br>
    thanks</p>