**9090**= 2 x 3 x 3 x 5 x 101.

**9090**has two representations as a sum of two squares:

**9090**= 21

^{2}+ 93

^{2}= 39

^{2}+ 87

^{2}.

**9090**is a divisor of 91

^{4}- 1.

**9090**is the number of centered 6-valent trees with 16 nodes (A036651).

Source: On-Line Encyclopedia of Integer Sequences