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numberphile
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NEW VIDEO: Goodstein Sequence

https://www.youtube.com/watch?v=0Le7NgS-wO0

Comments

I see. So, I made a mistake in the order of operation for the exponent. Thank you!

Hitoshi Yamauchi

3^3^3 is 3^27 - not 27^3

Numberphile

Unfortunately, I didn't get this. At 1:35, Is 3^3^3 equal to 19,683? It's just 27^3, which should be less than 100^3, which is one million. I think 3^3^3^3 is equal to 7,625,597,484,987. Is it really 3^3^3?

Hitoshi Yamauchi

The Wikipedia page mentions Dr. Goodstein! https://en.wikipedia.org/wiki/Knuth%27s_up-arrow_notation

Patrick W. Gilmore

I never did get "arrow notation" (Knuth arrows). Now I have to go back and watch the Graham's Number video to learn about them.

Patrick W. Gilmore

Nice video! It reminded me of the recently discovered "Antihydra" sequence, of which it is unknown - unlike the Goodstein sequences - whether it will ever halt or not: "Starting with the number 8, repeatedly add the number, divided by 2 (rounded down) to itself. So 8 -> 12 -> 18 -> 27 -> 40 -> 60 -> ... The resulting numbers are either even or odd. Will you eventually reach a number where you have generated more than twice as many odd as even numbers? If so, stop." If it does, this may take even more steps than any of the numbers mentioned in the video! It is the first/shortest unsolved turing machine (with only 6 states) and its mathematical and programmatic descriptions are equally very short. Yet, none of the researchers I've talked to expect it to be solved within the next 5 years! https://bbchallenge.org/antihydra https://www.sligocki.com/2024/07/06/bb-6-2-is-hard.html

coda


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