A single number followed by a comma in brackets

A single number followed by a comma in brackets, {n,}, means that the preceded regular expression is repeated at least n number of times. For example, to match the occurrence of the minimum 3 numbers between a and b in a line, we can use the following:

$ awk '/a[0-9]{3,}b/'  interval_regex.txt

The output on execution of the preceding code is as follows:

a123b
a1234b
a12345b
a1233456b
a111b
a111111b