I get OP was a joke, but I was trying to make a serious observation.

Say you have some kind of stochastic algorithm that works on the assumption it's fed a composite number most of the time. Maybe something like Pollard's Rho algorithm, where whatever number theoretic structure you need accumulates slowly over time as a result. You decide to just pick a large number at random for each iteration.

Implicitly, you've solved the problem of finding a composite number by assuming all (large) numbers are composite, like in this post. It is pretty close, like also mentioned in this post. If that's not good enough, you could also use a primality test that fails some small portion of the time, which do exist, and use less power than guaranteed tests.