57 is semiprime, being only divisible by exactly two prime numbers: 19 * 3
People, myself included before it became my favorite number, might just assume 57 is prime in a split second of considering off the top of their head, but mathematician Hermann Weyl incorrectly labeled 57 as a twin prime (with 59) in a published article (page 11).
57 is a Leyland number, which are numbers that can be written as x^y + y^x:
2^5 + 5^2 = 32 + 25 = 57
More coming soon...
While this site intends to be updated whenever I find more interesting stuff about the number 57, right now I've only just started with what I already have, so more should be coming relatively soon.