A formula that surely belongs here linking $\pi$ and the primes is $$2.3.5.7...=4\pi^2.$$ This is obtained via a zeta regularization in a similar way to the more well-known $\infty!=\sqrt{2\pi}$ (see e.g. herehere for a short discussion of this). However, to find the product of the primes, one uses the prime zeta function $$\sum_{p\; prime} \frac{1}{p^s}$$ which has the unfortunate property of having infinitely many singularities between 0 and 1 which breaks the standard regularization procedure. E. Muñoz García and R. Pérez Marco circumvent this problem (literally) by adding in an extra variable and taking the limit from a different direction.