108
This number is a composite.
108 = 22 * 33 (the product of the first two primes raised to themselves). [Sladcik]
The difference between the smallest (136) and second smallest (244) sums of squares (a^2 + b^2) where both a and b have more than one prime factor. [Hunter]
108 can be written as the sum of a cube and a square (a^3 + b^2) in two ways. [Hunter]
The concatenation of 108 with its previous and next number is prime, i.e., 108107 and 108109 are primes. [Bopardikar]
The smallest possible sum for a set of six distinct primes such that the sum of any five is prime: {5, 7, 11, 19, 29, 37}. [Honaker ,
Noe ,
Porter]
The sum of first 108 primes is prime. [Bajpai]
The concatenation of the first 108 positive integers that are squares or higher powers is a prime number. [Gaydos]