511/Historical Note

Historical Note on $511$

$511$ was the $1$st number of the form $2^n - 1$, where $n$ is odd, that was demonstrated to be composite.

This was done by Hudalrichus Regius in $1636$, who demonstrated that $2^9 - 1 = 511 = 7 \times 73$.

Sources

• 1919: Leonard Eugene Dickson: History of the Theory of Numbers: Volume $\text { I }$ ... (previous) ... (next): Preface