For a while I have been investigating the properties of a class of numbers that is related to Wieferich primes (those numbers are a 'pseudo'-superset of the Wieferich primes). I have been investigating the basic properties of those numbers and was able to prove some easy to determine properties of those numbers. With those properties in the bag, I wrote a small program in C++ that can search a given interval for those numbers. The program works (yay), but is still insanely slow. But, hey, better to have some slow but working code than prematurely optimized non-working code, not? I think some more theoretic results might also be useful in order to increase the search speed of the program, but those seem to be hard to obtain (at least for a geek like me).
Anyway, if you have written some number theoretic programs (excluding those used by PrimeGrid), feel free to talk about them in this thread (I am curious whether other people also use their spare time to write such programs even when those are not being used by a project such as PrimeGrid).