A simple C# function (and console app) to flatten an array down to a specified generic type

Program.cs

using System;
using System.Collections.Generic;

namespace ConsoleApp3
{
    // This is a sample Console App written in C# / .NET Core (but should work with .NET Framework).
    // This will flatten an array structure, recursively, down to the generic type specified (or throw an exception if the input is bad)
    
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");

            var a = new object[]
            {
                1, 
                2, 
                new object[]
                {
                    3,
                    new int[] 
                    { 
                        4, 
                        5 
                    }
                },
                6
            };

            var flatA = Flatten<int>(a);
            
            foreach (var item in flatA)
            {
                Console.WriteLine(item);
            }

            Console.ReadKey();

            // OUTPUT:
            //Hello World!
            //1
            //2
            //3
            //4
            //5
            //6

        }

        public static IEnumerable<T> Flatten<T>(Array input)
        {
            foreach (var item in input)
            {
                if (item is Array)
                    foreach (var flatItem in Flatten<T>((Array)item))
                        yield return flatItem;
                else
                    yield return (T)item;
            }
        }
    }
}