Counting variable name, which will get appended

I have some trouble with my web project. I'm looking for a solution how I can count my variable upwards in a loop. So that the name of the variable will go like this: panel1, panel2, panel3...

Thats my code

var panel = []
for(i=1; i<3; i++){
var $div = $('<div class="panel3" id="panel3">Box2 - 20</div>');
$('.panel[i]').append($div);
}

so the "panel[i]" at the bottom should get a higher number for every loop. I was looking a long time for a solution, but nothing worked.

The idea behind my code is to fill all those empty boxes with a div.

Some HTML

  <div class="panel-body">
  <!-- Reihe 1 -->
    <div class="row">
        <div class="col-md-2">
            <div class="panel1">
            </div>
        </div>
        <div class="col-md-2">
          <div class="panel2">
          </div>
        </div>

And so on...

Thanks for the help