25 (number)

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

[edit] In mathematics

It is a square number, being 5² = 5 × 5. It is the smallest square that is also a sum of two squares: 25 = 3² + 4². Hence it often appears in demonstrations of the Pythagorean theorem.

25 is a centered octagonal number and an automorphic number.

25 has an aliquot sum of 6 and is the first number to have an aliquot sequence that does not culminate in 0 through a prime. Twenty-five is the aliquot sum of three integers; 95, 119, and 143. Twenty-five is the second composite member of the 6-aliquot tree.

It is the smallest base 10 Friedman number as it can be expressed by its own numbers: 5².

It is also a Cullen number. 25 is the smallest pseudoprime satisfying the congruence 7ⁿ = 7 mod n. It is also a Somer pseudoprime based on 6.

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 least odd integer n such that there exist such that

where x_{n + 1} = x₁,x_{n + 2} = x₂.

Within base 10 one can readily test for divisibility by 25 by seeing if the last two digits of the number match 25, 50, 75 or 00.

[edit] In science

• The atomic number of manganese

[edit] 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).

[edit] In other fields

Twenty five is:

• 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 designation of United States Interstate 25, a freeway that runs from New Mexico to Wyoming
• The designation of the M25 London Orbital motorway
• Municipal Okrug 25, a municipal okrug of Kirovsky District of Saint Petersburg, Russia
• The (critical) number of Florida electoral votes for the 2000 U.S. presidential election
• The name of the national card game of Ireland and India (Pachisi — Hindi for 25)
• "25", a song by Veruca Salt from their 1994 album American Thighs
• "25th Floor", a song by Patti Smith Group from their 1978 album Easter
• Twenty Five is the name of a 2006 George Michael compilation celebrating 25 years in the music business (1981-2006)
• "25 boy", in Cantonese Chinese, is a slang term meaning "traitor" as used in the Chinese movie Over the Edge.
• The per-second frame rate of the PAL video standard
• The number of the French department Doubs

[edit] In sports

• The size of the full roster on a major league baseball team

[edit] Historical years

25 A.D., 25 B.C., 1925, 2025, etc.

Christmas is on the 25th of December