jquery validation only digits

$("#mobile_number").validate({
            rules: {

                mobile_number: {required: true,number:true}
            },
            messages: {
                mobile_number: {required: "Please Enter Your Mobile Number",number:"Please enter numbers Only"}
            }

 });

to check it add

$("#myform").validate({
  rules: {
    amount: {
      required: true,
      digits: true
    }
  }
});

http://docs.jquery.com/Plugins/Validation/Methods/digits