var banner = new Array();

banner[1]='https://i.servimg.com/u/f48/17/28/01/99/figura18.jpg';

document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];
setInterval("document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];",3000);