25 (number)

← 24 25 26 →
← 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-five
Ordinal	25th (twenty-fifth)
Factorization	52
Divisors	1, 5, 25
Greek numeral	ΚΕ´
Roman numeral	XXV
Binary	110012
Ternary	2213
Senary	416
Octal	318
Duodecimal	2112
Hexadecimal	1916

25 (twenty-five) is the natural number following 24 and preceding 26.

In mathematics

25 is a square.

It is a square number, being 5² = 5 × 5, and hence the third non-unitary square prime of the form p².

It is one of two two-digit numbers whose square and higher powers of the number also ends in the same last two digits, e.g., 25² = 625; the other is 76.

25 has an even aliquot sum of 6, which is itself the first even and perfect number root of an aliquot sequence; not ending in (1 and 0).

It is the smallest square that is also a sum of two (non-zero) squares: 25 = 3² + 4². Hence, it often appears in illustrations of the Pythagorean theorem.

25 is the sum of the five consecutive single-digit odd natural numbers 1, 3, 5, 7, and 9.

25 is a centered octagonal number, a centered square number, a centered octahedral number, and an automorphic number.

25 percent (%) is equal to ⁠1/4⁠.

It is the smallest decimal Friedman number as it can be expressed by its own digits: 5².

It is also a Cullen number and a vertically symmetrical number. 25 is the smallest pseudoprime satisfying the congruence 7ⁿ = 7 mod n.

25 is the smallest aspiring number — a composite non-sociable number whose aliquot sequence does not terminate.

According to the Shapiro inequality, 25 is the smallest odd integer n such that there exist x₁, x₂, ..., x_n such that

$\sum _{i=1}^{n}{\frac {x_{i}}{x_{i+1}+x_{i+2}}}<{\frac {n}{2}}$

where x_{n + 1} = x₁, x_{n + 2} = x₂.

Within decimal, one can readily test for divisibility by 25 by seeing if the last two digits of the number match 00, 25, 50, or 75.

There are 25 primes under 100: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.

F₄, H₄ symmetry and lattices Λ₂₄, II_25,1

Twenty-five 24-cells with $\mathrm {F_{4}}$ symmetry in the fourth dimension can be arranged in two distinct manners, such that

• in a 24-cell honeycomb, twenty-four 24-cells surround a single 24-cell, and where
• a faceting of the 600-cell with $\mathrm {H_{4}}$ symmetry can otherwise also be constructed, with cells overlapping.

The 24-cell can be further generated using three copies of the 8-cell, where the 24-cell honeycomb is dual to the 16-cell honeycomb (with the tesseract the dual polytope to the 16-cell).

On the other hand, the positive unimodular lattice $\mathrm {II_{25,1}}$ in twenty-six dimensions is constructed from the Leech lattice in twenty-four dimensions using Weyl vector

$(0,1,2,3,4,\ldots ,24|70)$

that features the only non-trivial solution, i.e. aside from $\{0,1\}$, to the cannonball problem where sum of the squares of the first twenty-five natural numbers $\{0,1,2,\ldots ,24\}$ in $\mathbb {N_{0}}$ is in equivalence with the square of $70$ (that is the fiftieth composite). The Leech lattice, meanwhile, is constructed in multiple ways, one of which is through copies of the $\mathbb {E_{8}}$ lattice in eight dimensions isomorphic to the 600-cell, where twenty-five 24-cells fit; a set of these twenty-five integers can also generate the twenty-fourth triangular number, whose value twice over is $600=24\times 25.$

In science

• The Standard Model of physics features a total of 25 elementary particles: 12 fermions (made of 6 quarks and 6 leptons) and 13 bosons (made of 12 gauge bosons and 1 scalar boson).
• The atomic number of manganese.
• The average percentage DNA overlap of an individual with their half-sibling, grandparent, grandchild, aunt, uncle, niece, nephew, identical twin cousin (offspring of identical twins), or double cousin.

In religion

• In Ezekiel's vision of a new temple: The number twenty-five is of cardinal importance in Ezekiel's Temple Vision (in the Bible, Ezekiel chapters 40–48).
• In Islam, there are 25 prophets mentioned in the Quran.

In sports

• Before 2020, the size of the full roster on a Major League Baseball team for most of the season, except for regular-season games on or after September 1, when teams expanded their roster to 40 players.
• The size of the playing roster on a Nippon Professional Baseball team for a particular game. Active NPB rosters consist of 28 players, but prior to each game, managers must designate three players who will be ineligible for that game.
• In baseball, the number 25 is typically reserved for the best slugger on the team. Examples include Mark McGwire, Barry Bonds, Jim Thome, and Mark Teixeira.
• The number of points needed to win a set in volleyball under rally scoring rules (except for the fifth set), so long as the losing team's score is two less than the winning team's score (i.e., if the winning team scores 25 points, the losing team can have no more than 23 points)
• In U.S. college football, schools that are members of NCAA Division I FBS are allowed to provide athletic scholarships to a maximum of 25 new football players (i.e., players who were not previously receiving scholarships) each season.

In other fields

Twenty-five is:

• The number of words in the American game show 25 Words or Less
• Part of the name of the LSD-25 molecule.
• The number of years of marriage marked in a silver wedding anniversary.
• The minimum age of candidates for election to the United States House of Representatives. "Under 25" provides a common cut-off point for designating youth.
• The number of cents in a quarter.
• The usual TCP port for SMTP.
• The name of the national board game of India (Pachisi — Hindi for 25).
• The name of an Irish card game, see Spoil Five.
• The per-second frame rate of the PAL video standard.
• The name of Adele's 2015 album 25, named for her age in that year.
• The number of the French department Doubs.
• The temperature, in Celsius, at which some characteristics of semiconductors are specifically given in a datasheet.
• The number of panels on the weekly TV Asahi quiz show Panel Quiz Attack 25.

Slang names

• Pony (British slang for £25)

Historical years

25 BC, AD 25, 1925, 2025 etc.

See also

• List of highways numbered 25