Composite Mersenne Number/Examples/M229/Historical Note

Historical Note on Mersenne Number $M_{229}$
Mersenne number $M_{229}$ was the largest of a set of $5$ demonstrated to be composite by using a manual desk calculator in the $1940$s.

The next Mersenne prime after $M_{127}$, proved prime in $1896$ by, does not occur until $M_{521}$.

As remarked, nobody had any idea that the next one would be so far away.

It is instructive to note that, in $2017$, it took a freely-available online factorization tool $4 \cdotp 8$ seconds to perform this exact calculation.