9 is an odd number.
9 is a palindrome.
9 is a Harshad number, which means it is divisible by the sum of its digits (9 = 9, and 9 is divisible by 9).
In binary, 9 is represented as 1001.
In hex, 9 is represented as 9.
9 is an Armstrong (or Narcissistic) number, which means it is the sum of its own digits each raised to the power of the number of digits.
Prime factorization of 9: 32.