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I always assumed that intuitively... I think the number is 20 people for the birthday paradox. 20 x 20 = 400, and there are ~365 days in a year. Is that how that works?


The actual number is 23: https://en.wikipedia.org/wiki/Birthday_problem

The square root approximation works well for large numbers, but leaves out some factors that are relevant for small numbers.


I was always surprised the math maths for birthdays. Human birthdays are not random, and cluster around various dates and seasonal patterns.


Here is a statistical analysis of birthdays https://www.zippia.com/advice/most-least-common-birthdays/


Doesn't the clustering make collisions strictly more likely?




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