Ez nem szebb? ^(?=\d(?:\d[A-Z]{3}|[A-Z]\d[A-Z]{2}|[A-Z]{2}\d[A-Z]|[A-Z]{3}\d)|[A-Z]\d(?:\d[A-Z]{2}|[A-Z]\d[A-Z]|[A-Z]{2}\d)|[A-Z]{2}\d(?:\d[A-Z]|[A-Z]\d)|[A-Z]{3}\d{2})(.)(?!\1)(.)(?!\1|\2)(.)(?!\1|\2|\3)(.)(?!\1\2\3\4).$ (De legalább rövidebb :)