BB(5)
BB(5) refers to the 5th value of the Busy Beaver function. In 1989, the 5-state busy beaver winner was found: a 5-state Turing machine halting after 47,176,870 giving the lower bound BB(5) ≥ 47,176,870[1].
In 2024, BB(5) = 47,176,870 was proven by the bbchallenge.org massively collaborative research project.
History
In this Section, we use Radó's original S (number of steps) and Σ (number of ones on the final tape) notations, see Busy Beaver Functions.
- In 1964, Green establishes Σ(5) ≥ 17.[2]
- In 1972, Lynn establishes S(5) ≥ 435 and Σ(5) ≥ 22.
- In 1973, Weimann establishes S(5) ≥ 556 and Σ(5) ≥ 40.
- In 1983, the Dortmund contestis organised to find new 5-state champions, winner is Uwe Schult who established S(5) ≥ 134,467 and Σ(5) ≥ 501.
References
- ↑ H. Marxen and J. Buntrock. Attacking the Busy Beaver 5. Bulletin of the EATCS, 40, pages 247-251, February 1990. https://turbotm.de/~heiner/BB/mabu90.html
- ↑ Pascal Michel. (2022). The Busy Beaver Competition: a historical survey. https://bbchallenge.org/~pascal.michel/ha#tm52