Primes
Calculate primes by using extremely fast sorting
... any kind of data. And as already mentioned, it's just the most efficient tree-based sorting algorithm that you can get.
But furthermore this way of finding primes interestingly leaves a hard nut to crack for mathematicians: In very rare cases it finds numbers that are not primes. For all primes below one million this phenomenon arises in exactly two cases:
31213 which is 7 * 7 * 7 * 7 * 13
336141 which is 3 * 3 * 13 * 13 * 13 * 17
Who can explain, why?