code: private static double calculateWidthDegrees(int n) {
          double a;
          if (n % 2 == 0)
              a = -1;
          else
              a = -0.5;
          double result = 180 / Math.pow(2, 2.5 * n + a);
          return result;
      }
docs: Returns the width in degrees of the region represented by a geohash of
  length n.
  
  @param n length of geohash
  @return width in degrees