Just some basic C# code for generating unique combinations from 1 to N

combination.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace StudyCode
{
    public static class Combination
    {
        public static List<int[]> Combinations(HashSet<int> availableNumbers, int[] currentArray, int index)
        {
            var result = new List<int[]>();

            if(availableNumbers.Count == 0)
                result.Add(currentArray);

            foreach(var number in availableNumbers)
            {
                var newArray = new int[currentArray.Length];
                currentArray.CopyTo(newArray, 0);

                var remaining = new HashSet<int>(availableNumbers);
                remaining.Remove(number);

                newArray[index] = number;
                result.AddRange(Combinations(remaining, newArray, index + 1));
            }

            return result;
        }

        public static List<int[]> CombinationsFor(int n) {

            return Combinations(new HashSet<int>(Enumerable.Range(1, n)), new int[n], 0);
        }
    }
}