[Deff]

<p><input type=text size="8"> <input type=button value="Факториал!" onclick=initSumF(this)></p>
<script type="text/javascript">

function Factorial(X) {
   if (X == 0 || X == 1) return 1;
   else return (X * Factorial (X - 1));
}
function SummFact(X) {
var sum = 0;
   for(var i =1; i<X+1; i++) {
       sum+=Factorial(i);
   } 
return sum;
}
function  initSumF(elem) {
   var elem=elem.parentNode.childNodes[0];

   if( +elem.value > 170){elem.value="error !";return}

   elem.value=SummFact(+elem.value);
}
</script>