238

238 = 2 x 7 x 17.

238 is the sum of the first 13 primes: 238 = 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19 + 23 + 29 + 31 + 37 + 41.

238 is the number of connected partial orders on six unlabeled elements.

238 is 11101110 in base 2 (binary). It is 3232 in base 4.

238 is a tridecagonal number (A051865).

U-238 is the non-fissile isotope of uranium that is the heaviest isotope of any material available through extraction from minerals.

Source: What's Special About This Number?