25 (number)
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25 (twenty-five) is the natural number following 24 and preceding 26.
| Cardinal | twenty-five |
| Ordinal | twenty-fifth |
| Factorization | <math>5^2 \,\!<math> |
| Roman numeral | XXV |
| Binary | 11001 |
| Hexadecimal | 19 |
In mathematics
It is a square number, being 52 = 5 × 5, and it is also the sum of two squares, 32 + 42, often used in demonstrations of the Pythagorean theorem. It is the smallest square that is also a sum of two squares. 25 is a centered octagonal number and an automorphic number.
It is the first/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-Lucas pseudoprime based on 6.
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.
In science
- The atomic number of manganese
In astronomy,
- Messier object M25, a magnitude 4.9 open cluster in the constellation Sagittarius
- The New General Catalogue object (http://www.ngcic.org/) NGC 25, a magnitude 11.9 barred spiral galaxy in the constellation Phoenix
- The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros1-175.html) of the solar eclipse series which began on -2051 April 19 and ended on -771 May 26. The duration of Saros series 25 was 1280.1 years, and it contained 72 solar eclipses.
- The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/LEsaros/LEsaros1-175.html) of the lunar eclipse series which began on -2038 August 6 and ended on -469 March 5. The duration of Saros series 25 was 1568.6 years, and it contained 88 lunar eclipses.
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, an American coin with George Washington's portrait on the obverse and an eagle on the reverse (or special reverses for the special state quarters since 1999), and a Canadian coin with Queen Elizabeth II on the obverse and a moose on the reverse (or special reverses lately).
- The designation of United States Interstate 25, a freeway that runs from New Mexico to Wyoming.
- The designation of the M25 London Orbital motorway.
- The (critical) number of Florida electoral votes for the 2000 U.S. presidential election.
- As of 2005, the number of member states of the European Union.
- Historical years: 25 A.D., 25 B.C., or (for example) 1925de:Fünfundzwanzig
es:Veinticinco fr:25 (nombre) ko:25 ia:25 it:Venticinque he:25 (מספר) nl:25 (getal) ja:25 no:25 (tall) pt:Vinte e cinco sl:25 (število) sv:25 (tal) zh:25