using System;

using System.Collections;

using System.Collections.Generic;

using Combinatorics;

using Combinatorics.Collections;

using System.Linq;

​

namespace ConsoleApp1

{

    class Program

    {

        private const int sum_target = 2020;

        private const int num_combos = 3;

        static void Main(string[] args)

        {

            var integers = new List<int>{1721, 979, 366, 299, 675, 1456};

            Combinations<int> c = new Combinations<int>(integers, num_combos, GenerateOption.WithoutRepetition);

            foreach (var v in c)

            {

                var sum = v.Sum();

                if (sum == sum_target)

                    Console.WriteLine($"Combination: {string.Join(",", v)} Sum: {sum} Product: {v.Aggregate(1, (acc, val) => acc * val)}");

            }

        }

    }

}