Prime Decomposition of 5th Fermat Number/Mistake

Source Work

1986: David Wells: Curious and Interesting Numbers:

The Dictionary

$641$

1997: David Wells: Curious and Interesting Numbers (2nd ed.):

The Dictionary

$641$

Mistake

Euler found the first counterexample to Fermat's conjecture that $2^{2^n} + 1$ is always prime, when he discovered in $1742$ that $2^{2^5} + 1$ is divisible by $641$.

The date was in fact $1732$.

In the entry for $257$, Wells gets the date right.

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $641$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $641$