https://en.wikipedia.org/wiki/Birthday_problem
In probability theory, the birthday problem asks for the probability that, in a set of n randomly chosen people, at least two will share a birthday.
A014088 Minimal number of people to give a 50% probability of having at least n coincident birthdays in one year.
Exact Solutions of the Generalized Birthday Problem https://oeis.org/A014088/a014088.txt