var imglist = new Array(
"../21.jpg","../22.jpg","../23.jpg","../24.jpg","../25.jpg","../26.jpg","../27.jpg","../28.jpg","../29.jpg");
var selectnum = Math.floor((Math.random() * 100)) % imglist.length;
var output = "<img src=" + imglist[selectnum] + ">";
document.write(output);