357

357 = 3 x 7 x 17.

357 is the only three-digit number such that 2*357³⁵⁷ - 1 is prime.

357 is the smallest three-digit number with its digits being three distinct odd primes that is not prime, nor do any of the permutations of its digits represent a prime number.

357 is the larger of the only two sphenic numbers (product of three distinct primes) consisting of three distinct prime digits.

357 is a divisor of 50² - 1.

The .357 Magnum is a revolver cartridge.

Source: Prime Curios!