**90**= 2 x 3

^{2}x 5.

**90**has a representation as a sum of two squares:

**90**= 3

^{2}+ 9

^{2}.

**90**is the smallest number that has six representations as a sum of four positive squares:

**90**= 1

^{2}+ 2

^{2}+ 2

^{2}+ 9

^{2}= 1

^{2}+ 2

^{2}+ 6

^{2}+ 7

^{2}= 1

^{2}+ 3

^{2}+ 4

^{2}+ 8

^{2}= 2

^{2}+ 5

^{2}+ 5

^{2}+ 6

^{2}= 3

^{2}+ 3

^{2}+ 6

^{2}+ 6

^{2}= 3

^{2}+ 4

^{2}+ 4

^{2}+ 7

^{2}.

**90**is 66 in base 14.

**90**degrees corresponds to east.

Source: WolframAlpha