Avoid Math.random() from looping the same number twice?

Question

I'm trying to play a random gallary image by making it stops at different frame every few seconds, and the actions is completely random.
The problem is, since there are only 5 different images(5 frames) I'm displaying, there is a high probability that it stays at the same frame, how do I avoid that? Like avoid staying at the same page twice, if not run the function again....?
setInterval(createItems,throwItems);
var RandomImg:randomImg =new randomImg();
RandomImg.y=100;
RandomImg.x=180;
RandomImg.gotoAndStop(Math.floor(Math.random()*(1+5-1))+1);//generate random value between 1-5
addChild(RandomImg);
Thanks

Answer 1

How do I keep track of the random value, like what value should I put within the if to compare?
I try modify it a little, and wrap it within an if(), and use preValue to track down the previous frame, am I doing it right?
setInterval(createItems,throwItems);
var preValue:Number;
function createItems():void
     var RandomImg:randomImg =new randomImg();
     var randomFrame= Math.floor(Math.random()*(1+5-1))+1; //generate random value between 1-5
     RandomImg.y=100;
     RandomImg.x=180;
     RandomImg.gotoAndStop(randomFrame);
     if(preValue == randomFrame)
          RandomImg.gotoAndStop(Math.floor(Math.random()*(1+5-1))+1);
          addChild(RandomImg);
          preValue = randomFrame;
     }else
                    addChild(RandomImg);
                    preValue = randomFrame;