jQuery(function() {
    jQuery("#datepicker1").datepicker();
});

<input type="text" id="datepicker1" name="datepicker1"/>

<?php $x++; ?>
<input type="text" id="datepicker<?=$x;?>" name="datepicker1"/>

$( "#datepicker1"  ).datepicker();
$( "#datepicker" ).datepicker("show");