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New Limits Set for Incomprehensible Busy Beaver Number BB(6)

9/14/2025

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Summary

Story summary

Researchers identified the first five busy beaver numbers: 1, 6, 21, 107, and 47,176,870.
The sixth number, BB(6), remains unknown but has staggering lower limits set in 2022.
BB(6) is so large it cannot be expressed in standard decimal notation.
Scott Aaronson highlights its incomprehensibility.
A contributor recently established a new lower limit for BB(6), advancing the Busy Beaver Challenge related to the halting problem.

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Story summary

Researchers identified the first five busy beaver numbers: 1, 6, 21, 107, and 47,176,870.
The sixth number, BB(6), remains unknown but has staggering lower limits set in 2022.
BB(6) is so large it cannot be expressed in standard decimal notation.
Scott Aaronson highlights its incomprehensibility.
A contributor recently established a new lower limit for BB(6), advancing the Busy Beaver Challenge related to the halting problem.