find formula

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

class Program
{
    public static IEnumerable<string> Formula(double[] numbers, bool[] used, double wanted, double last = 0)
    {
        if (Math.Abs(last - wanted) < 0.001)
        {
            yield return "";
            yield break;
        }
        for (int i = 0; i < numbers.Length; i++)
        {
            if (!used[i])
            {
                used[i] = true;
                var a = numbers[i];
                for (int j = 0; j < numbers.Length; j++)
                {
                    if (!used[j])
                    {
                        var b = numbers[j];
                        if (b > a || (a == b && j > i))
                        {
                            numbers[j] = a + b;
                            foreach (var s in Formula(numbers, used, wanted, numbers[j]))
                                yield return a + " + " + b + " = " + (a + b) + "\n" + s;
                            numbers[j] = a * b;
                            foreach (var s in Formula(numbers, used, wanted, numbers[j]))
                                yield return a + " * " + b + " = " + (a * b) + "\n" + s;
                        }
                        numbers[j] = a - b;
                        if (numbers[j] >= 0)
                            foreach (var s in Formula(numbers, used, wanted, numbers[j]))
                                yield return a + " - " + b + " = " + (a - b) + "\n" + s;
                        numbers[j] = a / b;
                        if (Math.Abs(numbers[j] - (int)numbers[j]) < 0.00001)
                            foreach (var s in Formula(numbers, used, wanted, numbers[j]))
                                yield return a + " / " + b + " = " + (a / b) + "\n" + s;
                        numbers[j] = b;
                    }
                }
                used[i] = false;
            }
        }
    }
    static void Main(string[] args)
    {
        var numbers = new double[] { 23, 46, 22, 74, 65 };
        var wanted = 829;
        // var numbers = new double[] {4,1,8,100,8,50};
        // var wanted = 589;
        numbers = numbers.OrderBy(a => a).ToArray();
        var used = numbers.Select(a => false).ToArray();
        var count = 0;
        var set = new HashSet<string>();
        foreach (var s in Formula(numbers, used, wanted))
        {
            count++;
            if (set.Add(String.Join("\n", s.Split('\n').OrderBy(a => a).ToArray())))
                Console.WriteLine(s);
        }
        Console.WriteLine(count);
        Console.WriteLine(set.Count);
    }
}