title: add a character in front of every element in a list
body: <p>I am making a calculator that factors a number. Currently, the list looks like this for the positive number <code>12</code>:<br>
   <code>[1,12,2,6,3,4,4,3,6,2,12,1]</code><br>
   I want to change the list, so it looks like this:<br>
  <code>[-1,-12,-2,-6,-3,-4,-4,-3,-6,-2,-12,-1]</code>.<br>
  How can I accomplish this?</p>