Smallest 3-Digit Permutable Prime
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Theorem
The smallest $3$-digit permutable prime is $113$.
Proof
- $113$ is prime.
- $131$ is prime.
- $311$ is prime.
Consider the $3$-digit primes smaller than $113$:
- $101, 103, 107, 109$
They all contain a zero.
Thus, for each of these, at least one permutation ends in a zero.
Hence it is divisible by $10$ and so is not prime.
$\blacksquare$
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $113$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $113$