Flatten array of ints c#

FlattenArray

using System;
using System.Collections.Generic;

namespace Playground
{
    class Program
    {
        static void Main(string[] args)
        {
            var result = new Solution().FlattenArray(new object[]
            {
                new object[]
                { 1, new object[]
                    { 2,3,4, new object[] { 5,6,7,8},
                        new object[] {9,10,new object[] { 11,12,13,14,15 },16,17 }
                    },
                    new object[] { 18,19,20,21,22,23}
                },
                new object[]{ 24,25,26,27 }
            });
            Console.Read();
        }
    }
    public class Solution
    {
        public int[] FlattenArray(object[] target)
        {
            var flatten = new List<int>();
            FlattenArrayRec(target, flatten);
            return flatten.ToArray();
        }
        private void FlattenArrayRec(object[] target, List<int> flatten)
        {
            for (int i = 0; i < target.Length; i++)
            {
                if (target[i] is int) { flatten.Add((int)target[i]); Console.WriteLine(target[i]); }
                else if (target[i] is object[]) FlattenArrayRec((object[])target[i], flatten);
                else throw new ArgumentException("Given argument contains invalid types.");
            }
        }
    }
}