C#-Code

using System;
using System.Collections.Generic;

namespace durch_1_30_teilbar {


	class Program {


		static decimal checkpoint = 100000000;
		static bool fertig = false;
		static int? limit = null;
		static void Main(string[] args) {

			while (!(limit > 1))
				try {
					if (limit != null) throw new FormatException();
					Console.Write("Teilbar durch 1 - ");
					limit = Convert.ToInt32(Console.ReadLine());
				}
				catch (FormatException) {
					Console.WriteLine("Bitte Gannzahl größer als 1 eingeben");
					limit = null;
					Console.ReadKey(false);
					Console.Clear();
				}

			List<Worker> liste = new List<Worker>();
			for (int i = 0; i < 4; i++) {
				liste.Add(new Worker((decimal)(limit * i + limit), i + 1, limit));
			}//2.329.089.562.800 (1-30)

			System.Threading.Tasks.Parallel.ForEach(liste, x => x.DoMath());

			Console.ReadKey(false);
		}

		class Worker {
			decimal diezahl;
			int id;
			int? limit;
			public Worker(decimal start, int id, int? limit) {
				diezahl = start;

				this.id = id;
				this.limit = limit;
			}


			public void DoMath() {

				bool found = false;

				try {
					while (!found) {
						found = true;
						for (int j = 2; j < limit; j++) {
							if (diezahl % j != 0) {
								found = false;
								break;
							}
						}


						if (diezahl > checkpoint) {

							Console.WriteLine(">{0:#,0.0} {1}", checkpoint / 1000000000, "Millarden");
							checkpoint = diezahl + 100000000;
						}
						
						if (found) break;
						diezahl += (decimal)(limit * 4);
						

						found = fertig;

					}
				}
				catch (Exception e) {
					found = false;
					Console.WriteLine(e.Message.ToString());
				}
				if (!fertig) {
					if (found) {
						Console.WriteLine("{0} ist durch 1-{1} teilbar", diezahl, limit);
						fertig = true;
					}
					else
						Console.WriteLine("Keine Zahl gefunden");
				}
			}
		}
	}
}