using System;
using System.Linq;
using System.Collections.Generic;
using System.Text.RegularExpressions;
public class Test
{
	public static void Main()
	{
		 var strs = new List<string> {"Some Words 1 2 3 4", "Some Words That Should not be replaced 12 9 123 4 12", "test 9 8", "t e s t 9 8", "Another 12 000" };
		 foreach (var test in strs) 
		 {
			Console.WriteLine(Regex.Replace(test, @"(?<=\d)\s+(?=\d)", ""));
		 }
		 
	}
}