Definition:Fermat Pseudoprime/Base 4/Mistake

Source Work

 * The Dictionary
 * $217$
 * $217$

Mistake

 * The second smallest pseudoprime to base $4$ ($15$ is the smallest).
 * $4^{216} - 1$ is divisible by $217$ although $217$ is not prime but $7 \times 31$.

Correction
The author is correct in that $217$ is indeed not prime, but $7 \times 31$.

Also, $15$ is the smallest pseudoprime to base $4$.

However, $217$ is not a pseudoprime to base $4$.

It is in fact the $3$rd pseudoprime to base $5$:
 * ''$5^{216} - 1$ is divisible by $217$.

In, this section has been removed.