[arcanemachiner]

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?

[twiss]

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.

[Spooky23]

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

[Vvector]

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

[whyever]

Doesn't the clustering make collisions strictly more likely?