code a number into letters
<p>Lets say I have something like 97463</p>

<p>I want to code it into letters say kljhs</p>

<p>I'm using php/javascript at the moment, but I guess its a universal problem.  </p>

<p>Whats the most efficient way to do this in a way thats reversible? </p>

<p>(reversible meaning given numbers I can make the letter code and then later given just the number code I can return the letters)</p>
