BB(2,5)
The 2-state, 5-symbol Busy Beaver problem BB(2,5) is unsolved. With the discovery of Hydra in May 2024, we now know that we must solve a Collatz-like problem in order to solve BB(2,5) and thus BB(2,5) is Hard.
The 2-state, 5-symbol Busy Beaver problem BB(2,5) is unsolved. With the discovery of Hydra in May 2024, we now know that we must solve a Collatz-like problem in order to solve BB(2,5) and thus BB(2,5) is Hard.