static int[] Eratosfen(int len)
        {
            bool[] table = new bool[len];

            for (int i = 0; i < table.Length; i++)
                table[i] = true;

            for (int i = 2; i * i < table.Length; i++)
                if (table[i])
                    for (int j = 2 * i; j < table.Length; j += i)
                        table[j] = false;

            int[] final = new int[0];
            int k = 0;
            for (int i = 2; i < table.Length; i++)
                if (table[i])
                {
                    Array.Resize(ref final, final.Length + 1);
                    final[k] = i;
                    k++;
                }
            return final;
        }