9090

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

9090 has two representations as a sum of two squares: 9090 = 21² + 93² = 39² + 87².

9090 is a divisor of 91⁴ - 1.

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

Source: On-Line Encyclopedia of Integer Sequences