$(function(){
var len = 3;
var arr = new Array(
"http://www.nikkei-azabu10.com/img/404a.jpg", 
"http://www.nikkei-azabu10.com/img/404b.jpg ", 
"http://www.nikkei-azabu10.com/img/404c.jpg "
);
var rand = Math.floor( Math.random() * len);
$("#e404 img").attr("src",arr[rand]);
});