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<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>
<body>
</body>
</html>
<script>
/*var a=prompt("请输入一个整数")
if(a==null)
{
}
else
{
var b=isNaN(a) ;
if (b==false)
{
var c=parseInt(a);
var sum=0;
for (var i=0;i<c;i++)
{
sum+=i;
}
document.write(sum)
}
else
{
alert(请输入整数)
}
}*/
var a=prompt("请输入一个整数")
if (a==null)
{
}
else
{
var b=isNaN(a);
if (b==false)
{
var sum =0;
var jie =1;
var c=parseInt(a);
for(var i=1; i<=c;i++ )
{
jie*=i;
sum+=jie;
}
document.write(sum)
}
else
{
alert("请输入整数")
}
}
</script>