title: Hexadecimal occurrence counting
body: <blockquote>
    <p>Write a PHP program with a function that given a value $n in input
    counts how many different number exist with all of the digits 0,1, and
    A present at least once for hexadecimal values from 1 to $n digits.</p>
  </blockquote>
  
  <p>I don't understand what this problem is fundamentally asking for.</p>
  
  <p>Let's say 1 to $n = 500. Are we counting the occurances of 0, 1, and A used in a hexadecimal anywhere from 1 to 500?
  I just can't seem to wrap my head around what is being asked to be counted.</p>