Single RegEx will probably not do exactly what you want (memory for pulling of that one might be big?). This is how I would do it: Let>STRING=;1;2;3;4;5;6;7;8;9;1;2;3;23;34;51; Let>REGEX_PATTERN=\b(\d+)\b(?=.*\b\1\b) RegEx>REGEX_PATTERN,STRING,0,FOUND,FOUND_count,0,, If>FOUND_count>0 Let>k=0 Repeat>...