It's not necessary to do so, just to simulate enough randomly drawn ones (from an approximation of the distribution of UFAIs that might have been created) that any particular deterrable UFAI assigns sufficient subjective probability to being in a simulation.

If one is restricted to even just finite calculations this is a very large set such that the probability that a UFAI should assign to being in a simulation should always be low. For example, off the top of my head it might be interested in 1) calculating large Mersenne primes 2) digits of Pi, 3) digits of Euler's contstant (gamma, not e), 3) L(2,X) where X is the quadratic Dirchlet character mod 7 (in this case there's a weird empirical identity between this and a certain integral that has been checked out to 20,000 places).And those are all the more well known options. Then one considers all the things specific people want as individuals. I can think of at least three relevant constants that I'd want calculated that are related more narrowly to my own research. And I'm only a grad student. Given how many mathematicians there are in the world, there are going to be a lot of examples in total. Sure, some of them, like digits of Pi, are obvious. But after that...