Any pattern followed by a {m,n}
allows the pattern to occur m to n times. So in your case \d{m,n}
for required values of m and n. If it has to be exactly an integer, use\d{m}
If you want to match 123 in x123y and not in 1234, use \d{3}(?=\D|$)(?<=(\D|^)\d{3})
It has a look ahead to ensure the character following the 3 digits is a non-digitornothing at all and a look behind to ensure that the character before the 3 digits is a non-digit or nothing at all.