Dart Regex memiliki setidaknya satu bilangan bulat
r'(^(?=.*\d))'
// For 6 to 20 use this:
r'(^(?=.*\d).{6,20}$)'
Defeated Dotterel
r'(^(?=.*\d))'
// For 6 to 20 use this:
r'(^(?=.*\d).{6,20}$)'