239 is a prime number. It is a Sophie Germain prime because 2 x 239 + 1 = 479, which is also a prime.
239 and 241 form a twin prime pair.
239 = 2 x 43 + 4 x 33 + 3 x 13.
239 and 23 are the only numbers that cannot be represented in fewer than nine positive cubes (the maximum).
239 needs four squares (the maximum) to express it and 19 fourth powers (the maximum) to express it. However, 239 doesn't need the maximum number of fifth powers.
The largest prime factor of n2 + 1 is at least 17, provided n is greater than 239.
The movie Pu-239, named for a radioactive isotope of the element plutonium, concerns a Russian nuclear plant worker.
Source: Wolfram MathWorld