24

← 23 25 → 24
← 20 21 22 23 24 25 26 27 28 29 → List of numbers — Integers 0 10 20 30 40 50 60 70 80 90 →
Cardinal	twenty-four
Ordinal	24th (twenty-fourth)
Factorization
Divisors	1, 2, 3, 4, 6, 8, 12, 24
Roman numeral	XXIV
Binary	110002
Octal	308
Duodecimal	2012
Hexadecimal	1816

24 (twenty-four) is the natural number following 23 and preceding 25.

The SI prefix for 10²⁴ is yotta (Y), and for 10^-24 (i.e., the reciprocal of 10²⁴) yocto (y). These numbers are the largest and smallest number to receive an SI prefix to date.

In mathematics

• 24 is the factorial of 4 and a composite number, being the first number of the form 2³q, where q is an odd prime.
• It is the smallest number with exactly eight divisors: 1, 2, 3, 4, 6, 8, 12, and 24. It is a highly composite number, having more divisors than any smaller number. Adding up all the proper divisors of 24 except 4 and 8 gives 24, hence 24 is a semiperfect number.
• Subtracting one from any of its divisors (except 1 and 2, but including itself) yields a prime number. 24 is the largest number with this property, for to have this property a number cannot be divisible by a prime greater than three, nor can it be divisible by 9 or 16.
• 24 has an aliquot sum of 36 and the aliquot sequence (24,36,55,17,1,0). Twenty-four is only the aliquot sum of one number the square 529.
• There are 10 solutions to the equation φ(x) = 24, namely 35, 39, 45, 52, 56, 70, 72, 78, 84 and 90. This is more than any integer below 24, making 24 a highly totient number.
• 24 is a nonagonal number. This number is also the sum of a twin prime (11 + 13). It is a Harshad number and a semi-meandric number.
• Together with the number one, 24 is one of the few numbers n for which the sum of μ(d)d² over the divisors d of n is equal to itself.^[1]
• The product of any four consecutive numbers is divisible by 24. This is because, among any four consecutive numbers, there must be two even numbers, one of which is a multiple of four, and there must be a multiple of three. ^[2]
• In 24 dimensions there are 24 even positive definite unimodular lattices, called the Niemeier lattices. One of these is the exceptional Leech lattice which has many surprising properties; due to its existence, the answers to many problems such as the kissing number problem and sphere packing are known in 24 dimensions but not in many lower dimensions. The Leech lattice is closely related to the equally nice length-24 binary Golay code and the Steiner system S(5,8,24) and the Mathieu group M₂₄. One construction of the Leech lattice is possible because of the remarkable fact that 1²+2²+3²+...+24² =70² is a perfect square; 24 is the only integer greater than 1 with this property. These properties of 24 are related to the fact that the number 24 also appears in several places in the theory of modular forms; for example, the modular discriminant is the 24th power of the Dedekind eta function.
• The Barnes-Wall lattice contains 24 lattices.
• 24 is the highest number n with the property that every element of the group of units (Z/nZ)^* of the commutative ring Z/nZ, apart from the identity element, has order 2; thus the multiplicative group (Z/24Z)^* = {1,5,7,11,13,17,19,23} is isomorphic to the additive group (Z/2Z)³. This fact plays a role in monstrous moonshine.
• The 24-cell, with 24 octahedral cells and 24 vertices, is a self-dual convex regular 4-polytope; it has no good 3-dimensional analogue.
• For any prime p greater than 3, p² − 1 is divisible by 24 with no remainder.

In science

• The atomic number of chromium
• The number of hours in a day

In religion

• The number of books in the Tanakh
• In Christian apocalyptic literature it represents the complete Church, being the sum of the 12 tribes of Israel and the 12 Apostles of the Lamb

In music

• There are 24 major and minor keys in Western tonal music, not counting enharmonic equivalents. Therefore, for collections of pieces written in each key, the number of pieces in such a collection; e.g., Chopin's 24 Preludes

In sports

• The number of Baseball Hall of Famer Willie Mays, retired by the San Francisco Giants.
• The number of Baseball Hall of Famer Tony Perez, retired by the Cincinnati Reds.
• The number of Baseball Hall of Famer Rickey Henderson, considered the greatest lead-off hitter of all-time.
• The number of former MLB All-Star Jimmy Wynn, retired by the Houston Astros.
• The car number of 4-time NASCAR Sprint Cup Series champion Jeff Gordon since the 1992 Hooters 500. Previously, another Gordon-- Cecil Gordon--had driven the 24 car.
• The jersey number of MLB All-Star and Gold Glove winner, Grady Sizemore from the Cleveland Indians
• The jersey number of MLB All-Star, Robinson Canó since the 2007 season.

• The current jersey number of NBA star, Kobe Bryant (from the 2006-07 season, onwards)
• The jersey number of NFL Stars, Champ Bailey,Michael Huff,Deltha O'neal,Ty Law,Charles Woodson,Cadillac Williams, and Marion Barber
• The number of teams that participated in each FIFA World Cup finals tournament between 1982 and 1994.
• The retired jersey number of Boston Bruins hockey joueur, Terry O'Reilly
• The jersey number of NHL Hall of Famer Bernie Federko, retired by the St. Louis Blues
• The number of accepted runners in the Melbourne Cup
• The number of Stanley Cups won by the Montreal Canadiens of the NHL.

In other fields

Astronomical clock in Prague

24 is also:

• The number of bits a computer needs to represent truecolour images (for a maximum of 16,777,216 colours). (But greater numbers of bits provide more accurate colors. "Truecolor" is one of many possible color representations.)
• The number of a broadcast television channel
• The number of Carats representing 100% pure gold.
• The number of cycles in the Chinese solar year.
• The number of frames per second at which motion picture film is usually projected.
• The number of hours in a day.
• The number of letters in both the modern and classical Greek alphabet. For the latter reason, also the number of chapters or "books" into which Homer's Odyssey and Iliad came to be divided.

• 24, television series starring Kiefer Sutherland. Each episode covers one hour, with 24 episodes making up one entire "day".
• The number of points on a backgammon board.
• When pronounced "two-four", a 24-pack of beer (Canadianism).
• A children's mathematical game involving the use of any of the 4 standard operations on 4 numbers on a card to get 24 (see Math 24)
• "24", a song by Welsh musician Jem
• The maximum number of Knight Companions in the Order of the Garter
• The Twenty-fourth Amendment to the United States Constitution is one of the Civil Rights-era amendments, abolishing poll tax requirements in federal elections.
• The designation of US Interstate 24, a freeway that runs from Tennessee to Illinois. Also many other roads called Route 24
• 24 is considered an unlucky number in Cantonese culture because its pronunciation is similar to that of "easy to die". For this reason, many buildings skip this floor number. The same goes for 13, 34, 44, etc.
• #24 is a recurring character on The Venture Bros.
• A Straight Edge symbol, for X is the 24th letter of the alphabet.
• The number of the French department Dordogne.
• In Brazil the number is associated with homosexuals due to the number representing the deer in the gambling game Jogo do Bicho and the word viado (a misspelling of veado, deer in Portuguese) being a slang for homosexuals.

Historical years

24 A.D., 24 B.C., 1924, 2024, etc.

References

External links

• My Favorite Numbers: 24, John C Baez