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
