# 25 (number)

 ← 24 25 26 →
Cardinal twenty-five
Ordinal 25th
(twenty-fifth)
Factorization 52
Divisors 1, 5, 25
Roman numeral XXV
Binary 110012
Ternary 2213
Quaternary 1214
Quinary 1005
Senary 416
Octal 318
Duodecimal 2112
Vigesimal 1520
Base 36 P36

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. 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 a centered octagonal number, a centered square number, and an automorphic number.

25 percent(%) is equal to 1/4.

25 has an aliquot sum of 6 and number 6 is the first (or smallest) 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.

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 $x_1, x_2, \dots, x_n$ such that

$\sum_{i=1}^{n} \frac{x_i}{x_{i+1}+x_{i+2}} < \frac{n}{2}$

where $x_{n+1}=x_1, x_{n+2}=x_2$.

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.

25 and 49 are the only perfect squares in the following list:

13, 25, 37, 49, 511, 613, 715, 817, 919, 1021, 1123, 1225, 1327, 1429, etc.

The formula in this list can be described as $10^n * Z + (2Z + 1)$ where n clearly depends on the number of digits in Z and in 2Z+1.

In base 30, 25 is a 1-automorphic number (displayed as the numeral 'P' or 'R' dependant on the chosen digit set), and in base 10 a 2-automorphic number.

## 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 twenty-five prophets mentioned in the Quran.

"Surrounding the throne were twenty-four other thrones, and seated on them were twenty-four elders. They were dressed in white and had crowns of gold on their heads."[1] Which means that there were 25 thrones.

## In sports

• 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 may expand their roster to no more than 40 players.
• In baseball, the number 25 is typically reserved for the best slugger on the team. Examples include Mark McGwire, Barry Bonds, 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.

Twenty five is:

## Slang names

• Pony (British slang for £25)[2]

## References

1. ^
2. ^ Evans, I.H., Brewer's Dictionary of Phrase and Fable, 14th ed., Cassell, 1990, ISBN 0-304-34004-9