<p>I’m getting 728…</p>
<p>It can have 1, 2 or 3 digits.</p>
<p>If it has 1 digit, there are 8 possibilites (1 thru 9, minus 7)</p>
<p>If it has two digits, there are 72 of them (8 choices for the tens, 9 for the ones, multiply).</p>
<p>If there are 3 digits, there are 648 of them (8 choices for the hundreds, 9 for the tens, 9 for the ones).</p>
<p>Add 'em up.</p>