Busy Beaver ones function value $\Sigma(5)$
--MULLIGANACEOUS--, via Wikimedia Commons. Public domain.
The maximal number of 1s that a $5$-state Turing machine can print on an initially blank tape before eventually halting.
Lower bound:
$4098$
Upper bound:
Unknown
Updates
-
1990-02
Lower bound: $4098$
Marxen, H., & Buntrock, J. (1990). Attacking the busy beaver 5. Bulletin of the EATCS, 40, 247-251.
[via The Busy Beaver Frontier, Scott Aaronson, 2020-09-29]