Wallisโ Formula
Hereโs a fun formula for Pi involving an infinite product, known as Wallisโ Formula:
(Pi/2) = (2*2)(4*4)(6*6)/(1*3)(3*5)(5*7)
It is somewhat surprising that when you pull out every other pair of terms, you get a completely different kind of number!
Sqrt[2] = (2*2)(6*6)(10*10)/(1*3)(5*7)(9*11)
https://math.hmc.edu/funfacts/wallis-formula/