Sixty-three (63, LXIII) is a natural number following sixty-two and preceding sixty-four. It is a composite number with the divisors being 3, 7, 9 and 21. Its factorization is:
- The atomic number of europium, a lanthanide.
- The code for international direct dial calls to the Philippines.
- The registry of the U.S. Navy's aircraft carrier USS Kitty Hawk (CV-63).