Definition:Fermat Pseudoprime/Historical Note
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Historical Note on Fermat Pseudoprime
From as far back as the ancient Chinese, right up until the time of Gottfried Wilhelm von Leibniz, it was thought that $n$ had to be prime in order for $2^n - 2$ to be divisible by $n$.
This used to be used as a test for primality.
But it was discovered that $2^{341} \equiv 2 \pmod {341}$, and $341 = 31 \times 11$ and so is composite.
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $341$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $341$