Integers: Recreation One (c#)

public static string ListSquared(long _m, long _n) {
            string result = "";

            int m=(int)_m, n=(int)_n;

            for (int i = m; i <= n; i++) {
                int range = Enumerable.Range(1, i).Where(x => i % x == 0).Sum(x => x * x);
                double round = Math.Sqrt(range);
                if (round == Math.Round(round)) {
                    string sum = string.Format("[{0}, {1}]", i.ToString(), range.ToString());
                    if (result == "")
                        result = sum;
                    else
                        result = result + ", " + sum;
                }
            }
            return "[" + result + "]";
        }