# 216,091/Historical Note

## Historical Note on $216 \, 091$

David Wells, in his Curious and Interesting Numbers of $1986$, announces that the Mersenne number $M_{261 \, 092} = 2^{261 \, 092} - 1$ was discovered by researchers at Chevron Geosciences of Houston, Texas, running performance tests on their Cray X-MP, in preparation for its use in oil prospecting.

It took $3$ hours, at $400$ million operations per second, to accomplish this feat, although the preliminary preparation to determine its possible primeness had taken several months beforehand.

An announcement about this was made on $18$ September $1985$, and, according to David Wells, was broadcast to Britain on BBC Radio.

However, it appears that David Slowinski had already discovered this fact on $1$ September $1985$, probably using the same (or a similar) configuration of the CRAY-1 he had used for previous searches.

Further research is needed into the exact details.