I have a machine which has four sequential cog wheels in constant mesh.
The largest cog has 81 teeth and the others have 52, 36 and 20 respectively.
What is the fewest number of revolutions the largest cog must make so that all of the cogs are back in their starting position?
[Ref: ZAVS] © Kevin Stone
Hint: Try breaking each cog size into prime factors.
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