I was reading about how people calculate millions, billions, and even trillions of digits of constants like $\pi$. All of these calculations use some implementation of a multiple precision arithmetic library such as GMP (GNU Multiple Precision). I was wondering if there were any other applications of these multiple precision arithmetic libraries involving calculations on numbers with greater than a million or so digits.
I know, especially in cryptography, that calculations with a few hundred to a few thousand digits are used, but I was wondering about computations with more digits then this?
Edit 1
I was just "browsing the internet" reading articles including this one here, http://plouffe.fr/simon/articles/1409.0091v1.pdf, as well as https://www.numberworld.org, and some this page here: https://www.craig-wood.com/nick/articles/pi-chudnovsky/.
The BBP formula can calculate the nth digit of pi in linear time. However, it can not be used to calculate the first n digits.