booksarr=new Array('020163466X','0764540483','1565845692','0596001053','0387026207','0072256559','0596005458','0131014056','0735623473','0764508466','1581601050','0787985112','0379113759','0028643216','');

if(booksarr.length > 6){
function getRndImg() {
  var rnd = Math.round(Math.random()*(booksarr.length-1));
  return booksarr[rnd]
}
function makeArray() {
  var list = "";
  var arr = new Array();
  cnt = 0;
  while (cnt!=nofRandom) {
    var img = getRndImg();
    if (list.indexOf(img)==-1) {
      arr[cnt++]=img
      list+=img;
    }
  }
  return arr;
}
nofRandom = 6;


arr = makeArray();
for (i=0;i<arr.length;i++)
    {document.write('<iframe src="http://rcm.amazon.com/e/cm?t=masternewmedi&o=1&p=8&l=as1&asins=' + arr[i]+ '&fc1=000000&IS2=1&lt1=_blank&lc1=0000FF&bc1=000000&bg1=FFFFFF&f=ifr" style="width:120px;height:240px;" scrolling="no" marginwidth="0" marginheight="0" frameborder="0"></iframe><br><br>')}

}