Classroom size	Total combinations (n)	Reproducible	Combinations with common birthday (ncommon birthday)	Probability of common birthday (Pcommon birthday)
2 students	3652 ≈ 133 k		365	$\frac{365}{365^2}=$ $0.27\%$
3 students	3653 ≈ 48.6 Μ		398 945	$\frac{398~945}{365^3}=$ $0.82\%$
4 students	3654 ≈ 17.7 Β		?	$\frac{?}{365^4}=$ $~~~~?~\%$
...	...		...	...