Pi
Speaking of useful things that computers can do – I have been noodling around the idea of calculating 100 trillion digits of Pi. The current record is 50 trillion digits.
The difficulty in the calculation is in the amount of memory needed to do the calculation. Using the Chudnovsky algorithm as implemented with the y-cruncher software I would need 503 TBs of working memory, plus an additional 160TBs for space to store the result.
It is not easy to get >500TBs of RAM, but it is possible to use disk storage in place of RAM. It slows down the calculation considerable, but reduces the cost to the problem of getting 660TBs of storage.
I figure 4x 16 drive cabinets of 12TB hard drives would do the trick, all connected over SAS to a 4 proc Xeon box with 1TB of RAM.
I am guessing it would take 14,100-20,000 compute hours (So close to 2 years running at full speed).
I already did 100 billion, and 1 trillion digits of Pi as a warm up.
What could I do with 100 trillion digits of Pi? What could you not do with that much coolness in one place. Perhaps I could find another number in this sequence: https://oeis.org/A057680