var oLetter = [
['e', 0.12652068126521], 
['t', 0.08760295720027], 
['a', 0.08009669873034], 
['o', 0.07856967112278], 
['n', 0.06967698093754], 
['h', 0.06122951107778], 
['s', 0.05911276181103], 
['r', 0.05644534529961], 
['i', 0.05595716511816], 
['d', 0.04211237517233], 
['l', 0.04123365084572], 
['u', 0.03121228808098], 
['m', 0.02655700187071], 
['c', 0.02282339984300], 
['y', 0.02123779061366], 
['w', 0.02044498599899], 
['f', 0.01982792624964], 
['g', 0.01812124833531], 
['p', 0.01544602094098], 
['b', 0.01155229581376], 
['v', 0.01004479541345], 
['I', 0.00927932888894], 
['k', 0.00684623886461], 
['A', 0.00258149679949], 
['T', 0.00209331661804], 
['G', 0.00208550573514], 
['M', 0.00180431395063], 
['x', 0.00167933982418], 
['B', 0.00159732555369], 
['P', 0.00157779834644], 
['Y', 0.00146844598579], 
['W', 0.00143329701273], 
['q', 0.00138643171531], 
['S', 0.00115601066967], 
['H', 0.00099979301160], 
['O', 0.00099979301160], 
['E', 0.00099198212870], 
['F', 0.00093730594838], 
['N', 0.00087481888515], 
['D', 0.00082795358773], 
['R', 0.00076546652451], 
['j', 0.00068735769548], 
['C', 0.00061705974935], 
['z', 0.00044131488403], 
['L', 0.00041007135242], 
['U', 0.00026166457726], 
['V', 0.00011716324355], 
['J', 0.00009373059484], 
['K', 0.00005077073887], 
['Q', 0.00005077073887], 
['Z', 0.00005077073887], 
['X', 0.00000781088290], 
  ]

  function getRandomLetter(bRand) {
    if (!bRand) {
      return (Math.floor(Math.random() * 26) + 10).toString(36);
    } else {
      while (true) {

        var nRandom = Math.random();
        for (var z = 0; z < oLetter.length; z++) {
          nRandom -= oLetter[z][1];
          if (nRandom <= 0) {
            return oLetter[z][0];
          }
        }

      }
    }
  }