This is really deja vu all over again. Over 45 years ago I read a "largest number that can be computed with expressions on a postcard" competition in a publication of some college (details escape me as to which college). This was held over a number of issues, and much of this discussion echoes (as far as I remember) that competition. Then, as now, the difficult part was comparing two values computed in completely different ways.
the difficult part was comparing two values computed in completely different ways
I think this is a lot of the fun. But if you wanted to make a similar contest that resolved more easily, what would you do?
Off the top of my head, maybe a contest to most closely approximate a huge non-Mersenne prime in n characters? (Edit: now that I think about it, I’m not sure that the computational complexity of numbers of c. largest-prime size would make that challenging enough for reasonable n. For example, the largest known non-Mersenne prime is apparently 19249·2^13018586+1 … boring.) Or maybe the best PRNG (under a given set of tests) in n characters?