327

327 = 3 x 109. The digits of 327 are themselves all primes.

327 is largest number n such that n, 2n, and 3n contain every digit from 1 to 9 exactly once: 327, 654, 981. In other words, the sum 327 + 654 = 981 contains each of the digits from 1 to 9 once.

327 is the number of 5s among the digits of all four-digit primes.

327 is a divisor of 76⁴ - 1.

327 is a number that cannot be written as a sum of three squares. It is the sum of four but no fewer squares.

The BMW 327 was a touring car produced between 1937 and 1941.

Source: What's Special About This Number?