Daniel Lemire's blog

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19 random digits is not enough to uniquely identify all human beings

Suppose that you assigned everyone a 19-digit number. What is the probability that two human beings would have the same number? It is an instance of the Birthday’s paradox.

Assuming that there are 8 billion people, the probability that at least two of them end up with the same number is given by the following table:

digits probability
18 99.9%
19 96%
20 27%
21 3%
22 0.3%
23 0.03%
24 0.003%
25 0.0003%

If you want the probability to be effectively zero, you should use 30 digits or so.