using System;

using IbanNet;

public class Program

{

    public static void Main()

    {

        var obfuscated = $"NL54INGBXXXXXXX503";

​

        var isIng = obfuscated.Contains("INGB");

​

        for (int i = 0; i < (isIng ? 999 : 999999); i++)

        {

            var iban = obfuscated.Replace("XXXXXXX", i.ToString().PadLeft(7, '0'));

​

            var validationResult = Iban.Validator.Validate(iban);

​

            if (validationResult.IsValid)

            {

                Console.WriteLine($"Possible IBAN found: {iban}");

            }

        }

​

        Console.WriteLine("Done!");

    }

}