http://pt.stackoverflow.com/questions/142932/verificar-se-string-inicia-com-numero/142937#142937

CSharp · Console

/Program.cs

using System;
using System.Text.RegularExpressions;
					
public class Program
{
	public static bool IsNumber(string str)
	{
    	return new Regex(@"^[0-9]+").IsMatch(str);
	}
	
	public static void Main()
	{
		Console.WriteLine(IsNumber("123"));
		Console.WriteLine(IsNumber("abc"));
		Console.WriteLine(IsNumber("1abc"));
		Console.WriteLine(IsNumber("a123"));
	}
}