175

This number is a composite.

175 = 1¹ + 7² + 5³. Note unity and the first four prime numbers.

The smallest number n greater than 1 such that n^6 + 6 is prime. [Rodrigo]

Smaller in the first pair of Honaker brothers {175, 176}.

The smallest composite number that forms two primes when its digits are sorted from low to high (157) and from high to low (751). The next two such composite numbers are 176 and 194. [Gaydos]