If memory serves me correctly, in Japan groups contain five things. If you had a half dozen eggs to sell, you would bill them as five plus one. I’m not sure why six isn’t as good as five, but I do know that groups of four are less desirable because the word for four, shi, sounds like death.
So, Japan being the world leader in giant robots, this is why all groups of robots that combine to form a larger robot consist of five robots.
This is pretty much the rule these days.
I’m sure some people realized the robots were going to combine to form a larger thing as soon as we introduced them. I’m less sure that people had their money on “Combine Harvester.”
–Geoff