90

90 = 2 x 3² x 5.

90 has a representation as a sum of two squares: 90 = 3² + 9².

90 is the smallest number that has six representations as a sum of four positive squares: 90 = 1² + 2² + 2² + 9² = 1² + 2² + 6² + 7² = 1² + 3² + 4² + 8² = 2² + 5² + 5² + 6² = 3² + 3² + 6² + 6² = 3² + 4² + 4² + 7².

90 is 66 in base 14.

As a compass direction, 90 degrees corresponds to east.

Source: WolframAlpha