BB(5)

With Fifth Busy Beaver, Researchers Approach Computation’s Limits

BB(5) has been verified to be equal to \(47,176,870\).

Years ago, when I was a student, I remember finding the University of Waterloo's "Handout on The Busy Beaver Problem" the easiest and most succinct introduction to the topic. Later, I found Dewdney's piece about busy beavers in the "The new Turing omnibus", perhaps a more famous source.

Remarkably, Waterloo's handout already contained the result from Marxen and Buntrock (1990), but it was a lower bound. Removing that ">" took 34 years. Here the table as presented in the handout: