L'ho risolta in questo modo:

codice:
<!doctype html><html lang="it">
  <head>
    <!-- Required meta tags -->
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">


    <!-- Bootstrap CSS -->
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
    <script type="text/javascript">
      function num_cons_mezz(val) {
        var new_inputs = '';
        for (var i = 1; i <= val ; i++) {
            new_inputs += '<label class="control-label col-sm-2" for="mezzi_c">Il consegnaotore numero '+i+' consegna:</label>'
            +'<div class="col-sm-10"> <label class="radio-inline"> <input type="radio" name="optradio'+i+'" checked>A piedi </label>'
            +' <label class="radio-inline"> <input type="radio" name="optradio'+i+'">In bici </label>'
            +' <label class="radio-inline"> <input type="radio" name="optradio'+i+'">In motorino </label> '
            +' <label class="radio-inline"> <input type="radio" name="optradio'+i+'">In macchina </label> </div>';
        }
        console.log(new_inputs);
        $('#mezzi_c').html(new_inputs);
      }
      
    </script>
    </head>
  <body><br><br>
  	 <div class="row form-group">
          <label class="control-label col-sm-2" for="num_c">Numero Consegnatori:</label>
            <div class="col-sm-10">
              <input type="number" class="form-control" id="num_c" placeholder="Numero Consegnatori" name="num_c" min="1"required="true" onchange="num_cons_mezz(this.value)">
            </div>
        </div>
          <div class="row form-group" id="mezzi_c">
          
        </div>
  </body>
  </html>
Grazie mille di avermi aiutato.