American [7]:
We all grow up learning that 13 is bad, and seven is good! But why has society decided this for us? Whose idea was this? Seven certainly doesn’t sound anything like “wealth,” “fortune,” or “prosper.” After doing some googling, the answer is definitely not as simple as I’d hoped. There are mathematical reasons, cultural reasons, religious reasons, etc. Frankly, there are too many random reasons to name, and they’re rather boring so I’m just going to link you to someone who has done all the work for me [here].