Composite Mersenne Number/Examples/M257/Historical Note

Historical Note on Mersenne Number $M_{257}$
Mersenne number $M_{257}$ was the largest Mersenne number conjectured by to be prime, in his  of $1644$.

In $1922$, demonstrated that it was composite, but did not find any actual factors.

Its full factorisation was eventually achieved by and.

It is instructive to note that, in $2017$, it took a freely-available online factorization tool $14 \cdotp 8$ seconds to perform this exact calculation.