Four

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: 2^{2}.