The Wallis Formula
π/2 is the infinite product of even #'s squared divided by its two adjacent oddspic.twitter.com/4iFKFIzuRm
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Hey - then you can write 2^2/(2^2 - 1) = 1 + 1/2^2 + 1/2^4 + .... 4^2/(4^2 - 1) = 1 + 1/4^2 + 1/4^4 + .... etc. and expand out the resulting huge product to get the sum of all products of all even powers of reciprocals of even numbers!
