Imports System

Public Module Module1

    Public Sub Main()

        Console.WriteLine(FormatLargeNumber("999999999999999999"))

    End Sub

​

    Private Function FormatLargeNumber(value As String) As String

        Dim myLong As ULong

        If (Not ULong.TryParse(value, myLong)) Then

            Throw New Exception("Invalid unsigned long.")

        End If

        Return myLong.ToString("#,##0")

    End Function

End Module