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CSharp · Console

/Program.cs

using System;
using System.Linq;
					
public class Program
{
	public static void Main()
	{
		int[] numbers1= { 1, 2, 3 };
		var numbers2 = numbers1.SelectMany(x => new[]{x,x,x});
		Console.WriteLine(String.Join(',',numbers2));
	}
}