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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.