4 is an even number.
4 is a palindrome.
4 is a Harshad number, which means it is divisible by the sum of its digits (4 = 4, and 4 is divisible by 4).
In binary, 4 is represented as 100.
In hex, 4 is represented as 4.
4 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 4: 22.