I think we need to outlaw dividing things by 17. Let’s make 17 the first and only Turboprime number. Not only is it not divisible by anything but one, but no other number is divisible by it.
It doesn't bother me only because i learned the "if it adds up to a number divisible by three it's divisible by three" trick really young so i automatically do it. Now, 91 bugs me!