Divisor of Fermat Number/Historical Note

Historical Note on Divisor of Fermat Number
In $1747$, proved that a divisor of a Fermat number $F_n$ is always in the form $k \, 2^{n + 1} + 1$.

This was later refined to $k \, 2^{n + 2} + 1$, the result given here, by.