425

425 = 5² x 17.

425 has three representations as a sum of two squares: 425 = 5² + 20² = 8² + 19² = 13² + 16².

425 is the hypotenuse of two primitive Pythagorean triples: 425² = 87² + 416² = 297² + 304².

425 is a pentagonal number, a number of the form n(3n - 1)/2, where n = 17.

425 is the number of subsets of {1, 2, 3, . . . 11} that have an integer average.

425 is the telephone area code for suburbs to the north and east of Seattle, Washington.

Source: What's Special About This Number?