How do you find a duck number?

A duck number is defined as a positive number that has zeroes present in it but does not start with a zero. To determine if a number is a duck number, check its digits: if it contains at least one '0' and the first digit is not '0', then it qualifies as a duck number. For example, 1023 and 507 are duck numbers, while 0123 and 1230 are not.