Busy Beaver ones function value $\Sigma(6)$
The maximal number of 1s that a $6$-state Turing machine can print on an initially blank tape before eventually halting.
Lower bound:
$3.5\times10^{18267}$
Upper bound:
Unknown
Updates
-
2011
Lower bound: $3.5\times10^{18267}$
Kropitz, P. (2011). Problém busy beaver.
[via The Busy Beaver Frontier, Scott Aaronson, 2020-09-29]