NumberOfDivsToRandomDisplay = 3;

var CookieName = 'DivRamdomValueCookie';
function DisplayRandomDiv() {
var r = Math.ceil(Math.random() * NumberOfDivsToRandomDisplay);
if(NumberOfDivsToRandomDisplay > 1) {
   var ck = 0;
   var cookiebegin = document.cookie.indexOf(CookieName + "=");
   if(cookiebegin > -1) {
	  cookiebegin += 1 + CookieName.length;
	  cookieend = document.cookie.indexOf(";",cookiebegin);
	  if(cookieend < cookiebegin) { cookieend = document.cookie.length; }
	  ck = parseInt(document.cookie.substring(cookiebegin,cookieend));
	  }
   while(r == ck) { r = Math.ceil(Math.random() * NumberOfDivsToRandomDisplay); }
   document.cookie = CookieName + "=" + r;
   }
for( var i=1; i<=NumberOfDivsToRandomDisplay; i++) {
   document.getElementById("randomdiv"+i).style.display="none";
   }
document.getElementById("randomdiv"+r).style.display="block";
}
DisplayRandomDiv();