Formatting numbers

Program.cs

using System;
using System.Linq;

namespace NumberFormatter
{
    class Program
    {
        private static Formatter formatter = new Formatter();
        static void Main(string[] args)
        {
            var numbers = new double[] { 10, 1234, 15000, 7500000, 19291921, 129312932193219, 1239812379128379281, 12389721983721983217111d };
            var numbersFormatted = numbers.Select(formatter.Format).ToArray();
            Console.WriteLine(String.Join("\n", numbersFormatted));
        }

    }

    public class Formatter
    {
        private string[] names = new string[] { "k", "million", "billion", "trillion", "quadrillion", "quintilion", "sextillion" };
        public string Format(double d)
        {
            for (var i = names.Length - 1; i >= 0; i--)
            {
                var limit = Math.Pow(10, (i + 1) * 3);
                if (d >= limit)
                {
                    return (d / limit).ToString("f3") + " " + names[i];
                }
            }

            return d.ToString();
        }
    }
}