Bootstrap datetimepicker is not a function

The problem is that you have not included bootstrap.min.css. Also, the sequence of imports could be causing issue. Please try rearranging your resources as following:

<link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" />
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.37/css/bootstrap-datetimepicker.min.css" />

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.10.6/moment.min.js"></script>                       
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.37/js/bootstrap-datetimepicker.min.js"></script>

DEMO


Below is the right code. Include JS files in following manner:

$(document).ready(function() {
  $(function() {
    $('#datetimepicker6').datetimepicker();
    $('#datetimepicker7').datetimepicker({
      useCurrent: false //Important! See issue #1075
    });
    $("#datetimepicker6").on("dp.change", function(e) {
      $('#datetimepicker7').data("DateTimePicker").minDate(e.date);
    });
    $("#datetimepicker7").on("dp.change", function(e) {
      $('#datetimepicker6').data("DateTimePicker").maxDate(e.date);
    });
  });
});
<html>

<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">

<!-- Optional theme -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap-theme.min.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.37/css/bootstrap-datetimepicker.min.css" />

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.10.6/moment.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>

<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.37/js/bootstrap-datetimepicker.min.js"></script>

<body>



  <div class="container">
    <div class='col-md-5'>
      <div class="form-group">
        <div class='input-group date' id='datetimepicker6'>
          <input type='text' class="form-control" />
          <span class="input-group-addon">
                        <span class="glyphicon glyphicon-calendar"></span>
          </span>
        </div>
      </div>
    </div>
    <div class='col-md-5'>
      <div class="form-group">
        <div class='input-group date' id='datetimepicker7'>
          <input type='text' class="form-control" />
          <span class="input-group-addon">
                        <span class="glyphicon glyphicon-calendar"></span>
          </span>
        </div>
      </div>
    </div>
  </div>



</body>


</html>