title: SymPy - Treating numbers as symbols
body: <p>How can I treat numbers as symbols in SymPy?</p>
  
  <p>For example, if I am performing a factorization with symbols I get:</p>
  
  <pre class="lang-py prettyprint-override"><code>from sympy import factor
  factor('a*c*d + a*c*e + a*c*f + b*c*d + b*c*e + b*c*f')
  c*(a + b)*(d + e + f)
  </code></pre>
  
  <p>I would like the same behaviour when I am using numbers in the expression.
  Instead of</p>
  
  <pre class="lang-py prettyprint-override"><code>from sympy import factor
  factor('2006*c*d + 2006*c*e + 2006*c*f + 2007*c*d + 2007*c*e + 2007*c*f')
  4013*c*(d + e + f)
  </code></pre>
  
  <p>I would like to get</p>
  
  <pre class="lang-py prettyprint-override"><code>from sympy import factor
  factor('2006*c*d + 2006*c*e + 2006*c*f + 2007*c*d + 2007*c*e + 2007*c*f')
  c*(2006 + 2007)*(d + e + f)
  </code></pre>