using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        int[] arr = new int[]{2,4,6,9};          

        string str = String.Join(",", arr.ToList().ConvertAll(i => "["+i.ToString()+"]").ToArray());

​

        Console.WriteLine(str);

    }

}