Challenge the legendary Gianfranco Borghetti! He can perform complicated and intricate calculations in nanoseconds (it took him only very few seconds to find the answer to the following division: 65748:34!). If you ask him "Gianfranco, what day was it on August 30th, 1567?" he will instantly tell you that it was a Saturday, and if that is in the Gregorian or Julian calendar; and he'll do it for any date! If you don't believe it, look at this video; he explained the math to us, but we can assure you that it is quite involved. Have fun!
If someone wants to challenge him, let him or her prepare and we will organize the match, Gianfranco is ready any time!