Probability 33 people in a group of 100,000 have the same birthday? Assuming years have 365,000 days. Would this Poisson Formula work?
Updated!
Note to OP: Probability of exactly $33$ people have the same birthday? Or probability of at least $33$ people have the same birthday? Or probability that exactly $33$ people have the same birthday and possibly another group of $33$ has the same (but different) birthday? Or probability that a given preselected group of 33 people have the same birthday? Or.....