Rational Numbers That Are Hard To Prove?

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Discussion Overview

The discussion revolves around the question of rational numbers that have been difficult to prove as rational over extended periods. Participants explore examples of numbers whose rationality status was uncertain for decades before being established, as well as the challenges in identifying such numbers.

Discussion Character

  • Exploratory, Debate/contested, Historical

Main Points Raised

  • One participant notes that many constants, such as pi and e, are believed to be irrational, and questions whether there are examples of numbers whose rationality was unknown for a long time before being proven rational.
  • Another participant argues that it is unlikely to find such examples, suggesting that the description of numbers tends to either fall within the realm of rationals or be complex enough to suggest irrationality or transcendence.
  • A participant mentions Legendre's constant, which was introduced in 1808 and proven to be rational in 1899, as a historical example of a number whose rationality was established after a significant period of uncertainty.
  • The same participant references a related problem that led to a question about the lower limit of a constant, which was shown to be zero in 2005, indicating ongoing exploration in this area.

Areas of Agreement / Disagreement

Participants express differing views on the likelihood of finding rational numbers that remained unproven for extended periods, with some suggesting it is unlikely while others provide historical examples.

Contextual Notes

The discussion highlights the complexity of defining numbers and the implications this has on their rationality, as well as the historical context of certain constants and their proofs.

Office_Shredder
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There are lots of examples of numbers where "is it a rational number" has been an open question for a while before being proved as not being rational. Pi and e being famous examples. Some of them are still open, like pi+e, or the Euler-Mascharoni constant, but I think the general consensus is that constants like these almost surely are going to be irrational. So I was wondering are there any examples of numbers whose rationality was unknown for an extended period of time (Beyond the first time the question was raised would be interesting, but something on the order of decades would be really nice) before it was discovered that the number is rational?
 
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This is rather unlikely. The problem comes with the question itself: you have to describe the number somehow. And this description is either within rationals or so complex, that it is almost certainly irrational, if not transcendent. I thought of something like the matrix exponent, the lower bound for the complexity of matrix multiplication, but it is unknown. And so are probably all interesting examples.
 
Legendre's constant was introduced 1808. It was shown to be exactly 1 (and therefore rational) in 1899.

This problem lead to the question what the lower limit on c is (Erdős, 1940). The answer is 0 (shown 2005).

There is some other more famous constant where I don't find the name now that is suspected to be exactly zero.
 
mfb said:
Legendre's constant was introduced 1808. It was shown to be exactly 1 (and therefore rational) in 1899.

This problem lead to the question what the lower limit on c is (Erdős, 1940). The answer is 0 (shown 2005).

There is some other more famous constant where I don't find the name now that is suspected to be exactly zero.
1798 (Legendre) 1849 (Chebyshev)
 

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