54

This number is a composite.

The sum of the non-prime divisors of 54 is a Mersenne prime exponent. [Noll]

The 54^th prime is the smallest number that is the sum of three cubes in two ways. [Noll]

The sum of denoninators of the Bernoulli numbers less than or equal to 54 is prime. [Noll]

13⁵⁴ + 54 is prime. [Noll]

(54!/45!)-1 is prime. [Patterson]

7^54+54^7 is the only non-titanic prime of form 7^n+n^7. [Loungrides]