Format string with dashes

I would approach this by having your own formatting method, as long as you know that the "Parcel Number" always conforms to a specific rule.

public static string FormatParcelNumber(string input)
{
  if(input.length != 12)
     throw new FormatException("Invalid parcel number. Must be 12 characters");

  return String.Format("{0}-{1}-{2}-{3}-{4}",
                input.Substring(0,2),
                input.Substring(2,2),
                input.Substring(4,2), 
                input.Substring(6,3), 
                input.Substring(9,3));
}

This should work in your case:

string value = "410151000640";
for( int i = 2; i < value.Length; i+=3){
  value = value.Insert( i, "-");
}

Now value contains the string with dashes inserted.

EDIT

I just now saw that you didn't have dashes between every second number all the way, to this will require a small tweak (and makes it a bit more clumsy also I'm afraid)

string value = "410151000640";
for( int i = 2; i < value.Length-1; i+=3){
  if( value.Count( c => c == '-') >= 3) i++;
  value = value.Insert( i, "-");
}

If its part of UI you can use MaskedTextProvider in System.ComponentModel

    MaskedTextProvider prov = new MaskedTextProvider("aa-aa-aa-aaa-aaa");
    prov.Set("41x151000a40");
    string result = prov.ToDisplayString();

Here is a simple extension method with some utility:

    public static string WithMask(this string s, string mask)
    {
        var slen = Math.Min(s.Length, mask.Length);
        var charArray = new char[mask.Length];
        var sPos = s.Length - 1;
        for (var i = mask.Length - 1; i >= 0 && sPos >= 0;)
            if (mask[i] == '#') charArray[i--] = s[sPos--];
            else
                charArray[i] = mask[i--];
        return new string(charArray);
    }

Use it as follows:

        var s = "276000017812008";
        var mask = "###-##-##-##-###-###";
        var dashedS = s.WithMask(mask);

You can use it with any string and any character other than # in the mask will be inserted. The mask will work from right to left. You can tweak it to go the other way if you want.

Have fun.

If i understodd you correctly youre looking for a function that removes all letters from a string, aren't you?

I have created this on the fly, maybe you can convert it into c# if it's what you're looking for:

Dim str As String = "410151000vb640"
str = String.Format("{0:##-##-##-###-###}", Convert.ToInt64(MakeNumber(str)))


Public Function MakeNumber(ByVal stringInt As String) As String
    Dim sb As New System.Text.StringBuilder
    For i As Int32 = 0 To stringInt.Length - 1
        If Char.IsDigit(stringInt(i)) Then
            sb.Append(stringInt(i))
        End If
    Next
    Return sb.ToString
End Function