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How long can a Turing machine program run when started on the blank tape before the tape becomes blank again? Of course, this will depend on the length of the program – how many states and colors it has. Even given these parameters, it is logically impossible to calculate how long a self-cleaning Turing machine can run. Any values that can be known have to be discovered empirically.
2×10^10^10^18,705,352 (“Wythagoras” 2014) As you can see, the function is reasonably under control for n≤4, then “achieves liftoff” at n=5. In my survey, inspired by a suggestion of Harvey Friedman, I defined a variant called Beeping Busy Beaver, or BBB. Define a beeping Turing machine to be a TM that has a single designated state where it emits a “beep.” The beeping number of such a machine M, denoted b(M), is the largest t such that M beeps on step t, or ∞ if there’s no finite maximum. Then BBB(n) is the largest finite value of b(M), among all n-state machines M.