375

375 = 3 x 5³.

375 is a number that cannot be written as a sum of three squares.

375 is a 5-smooth number. The product of its prime factors equals its sum of digits: 5 x 3 = 3 + 7 + 5 = 15.

Its odd powers end with 375, and its even powers end with 625.

The year 2010 is the 375th anniversary of the founding of the town of Newbury, Massachusetts.

Source: Prime Curios!