jQuery ajax return value

How can I return the value "pinNumber" from jquery ajax so I can append it outside of the ajax. Here is my code

var x = pinLast + 1;
    for(i=x;i<=pinMany;i++) {
        var i = x++;
        var cardNumber = i.toPrecision(8).split('.').reverse().join('');
        var pinNumber = '';

        jQuery.ajax({
            type: "POST",
            url: "data.php",
            data: "request_type=generator",
            async: false,
            success: function(msg){
                var pinNumber = msg;
                return pinNumber;
                //pin number should return
            }
        });

        jQuery('.pin_generated_table').append(cardNumber+' = '+pinNumber+'
');
        // the variable pinNumber should be able to go here

    }

Please ask me if you don't understand.. ^^ thanks