69 and 6174

Two new videos have gone up this week for the Numberphile project.

They are 69 and 6174.

The first to be uploaded was 6174, featuring Professor Roger Bowley's discussion of the so-called Kaprekar Constant.



For the second video this week I let the public decide via a vote on Facebook - the options were 31, 69 and 153.

Perhaps unsurprisingly, the choice was 69.

In this video Professor Laurence Eaves discusses why 69 is the highest number you can factorialize on a standard pocket calculator.



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