Can not convert 17 digit Number to String

I am facing issue in Number to String Conversion. I am using flex 4.5 SDK

I have 17 digit numbers and when i try to convert in to string then it is not giving me proper result.

Var myNumber :Number = 64336512942563914;

Var myString:String  = myNumber.toString();

trace(“myString ”+myString);

trace(“myNumber ”+myNumber);

//out put :

myString 64336512942563910

myNumber 64336512942563910

Its automatically converts 17^th digit to “0” value

I have also tried type conversion(Srting(myNumber)) but no Luck same problem ,

Also tried directly displaying number in the trace()  function same problem I am getting 

Is this issue in the Flex Sting Class?