//求斐波那契数列第n位
var n = parseInt(window.prompt('输入你要求的斐波那契数列的位数'));
var first = 1,
  second = 1,
  third;
if (n > 2) {
  for (var i = 0; i < n - 2; i++) {
    third = first + second;
    first = second;
    second = third;
    document.writeln('斐波那契数列的第' + (i + 3) + '位是：' + third)
  }
} else {
  document.writeln(1);
}

 //倒序输出
 var n = window.prompt("请输入三位数的整数");
 for (var i = n.length; i >= 0; i--) {
   document.writeln(n.charAt(i));
 }
 document.writeln(a);

//判断是否质数
var count = 0; //计数器
for (var i = 1; i < 100; i++) {
  //看每个i是否质数
  for (var j = 1; j <= i; j++) {
    if (i % j == 0) {
      //统计被整除的次数
      count++;
    }
  }
  //如果被整除的次数等于2次，则输出这个数
  if (count == 2) {
    document.writeln(i + " ");
  }
  //计数器清零
  count=0;
}