Sixty-three is a natural number following 62 and preceding 64.

Cardinal	sixty-three
Ordinal	63rd (sixty-third)
Factorization
Divisors	3, 7, 9, 21
Roman numeral	LXIII
Binary	111111
Hexadecimal	3F

In mathematics

Although a number of the form 2ⁿ - 1, 63 is technically not a Mersenne number since n is not prime and 63 is certainly not prime either. It is a Woodall number and a Harshad number. It is a highly cototient number.

In science

• The atomic number of europium, a lanthanide

In astronomy,

Messier object M63, a magnitude 8.5 galaxy in the constellation Canes Venatici, also known as the Sunflower Galaxy.

The New General Catalogue object NGC 63 , a spiral galaxy in the constellation Pisces

The Saros number of the solar eclipse series which began on -879 April 20 and ended on 401 May 29. The duration of Saros series 63 was 1280.1 years, and it contained 72 solar eclipses.

The Saros number of the lunar eclipse series which began on -758 October 12 and ended on 739 March 29. The duration of Saros series 63 was 1496.5 years, and it contained 84 lunar eclipses.

In other fields

Sixty-three is:

• 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).
• The number of the French department Puy-de-Dôme.
• The year AD 63, 63 BC, or 1963.