Nine is the width of Og Melech Haboshon’s bed, or crib. Nine is also the notes in Missorsky’s atonal scale.
The ibn Ezra writes that if you make two columns of the numbers until nine you get the product of nine multiplied by each. For example, 9*1 = 9, 9*2 = 18, 9*3 = 27, 9*4 = 36. The same is for the other way, 9*6 = 54, 9*7 = 63, 72, 81, 90.