function randomNum(low, high) 
{ 
    return Math.random()*(high-low) + low; 
}  

function randomInt(low, high) 
{ 
    return Math.floor(Math.random()*(high-low+1)) + low; 
}  

function randomChar(str) 
{  
    return str.charAt(randomInt(0, str.length-1)); 
}  

function randomOneOf(list) 
{    
    return list[randomInt(0, list.length-1)]; 
} 

 function generateRandSeq(len, letters)
  {
      var i, seq = "";
      for (i = 1; i <= len; i = i + 1) {
          seq += randomChar(letters);
      }
      return seq;
  }