Factorial

function factorial(n):Number { 
 if (n < 2) {
  return 1;
 }
 return n*factorial(n-1);
}

trace(factorial(3)); //Outputs 6

Generate Random Number

function randomRange(max:Number, min:Number = 0):Number
{
     return Math.round(Math.random() * (max - min)) + min;
}

trace(randomRange(5)); //Outputs number between 0 and 5
trace(randomRange(10,1)); //Outputs number between 1 and 10