regex search to find a string when it repeats X number of times

If you want to run a regular expression for a string which appears at least X times successively, you can run this search:

^(?!(.*?x){4})(?=.*x).*$

This search will find the string 'X', entered after the first ? and then at the end of the second parentheses, whenever it appears Y number of times successively, Y being one less than the number entered in the curly brackets.