Comment by constantcrying

>but there is no need to use it in any application.

Applications such as planes flying, sending data through wires, medical imaging (or any of a million different direct applications) do not count, I assume?

Your naivety about what makes the world function is not an argument for something being useless. The number appearing in one of the most important algorithms should give you a hint about how relevant it is https://en.wikipedia.org/wiki/Fast_Fourier_transform