Literally it's all you need to read to understand how maps work (though quite hard to get through, but defenetly worth it)

best brain)

391 is not a prime number.

Backwards Read Primes are primes that when read backwards in base 10 (from right to left) are a different prime.

I stumbled on this one myself.
The description states that all characters should be treated as upper case.

If you add up the ascii values for each string, they're equal. They each equal 360.