23,209/Historical Note

Historical Note on $23 \, 209$
The Mersenne number $M_{23 \, 209} = 2^{23 \, 209} - 1$ was demonstrated to be a Mersenne prime on $9$ February $1979$ by, using the same CDC-CYBER-174 that he and used to discover the primality of $M_{21 \, 701}$.

It took the computer $8$ hours to check the number.

$2$ weeks later, used a CRAY-1 supercomputer to check the result, and it took $7$ minutes.