86,243/Historical Note

Historical Note on $86 \, 243$
The Mersenne number $M_{86 \, 243} = 2^{86 \, 243} - 1$ was demonstrated to be a Mersenne prime on $25$ September $1982$ by, using a CRAY-1 supercomputer.

Working at $150$ megaflops, it took $1$ hour, $3$ minutes and $22$ seconds for this calculation to be performed, but several months of preliminary work to establish that this number was indeed likely to be prime.

According to, writing in in $1986$, a mere $150$ megaflops was already old hat by then, and the more recent models available at that time could work at anything up to $1000$ megaflops.

In a final sentence of gosh-wowery, his jaw drops to the floor to report that the Cray-3 was expected to reach the order of $10$ gigaflops.

However, that machine was never commercially available, and the line was discontinued.