25 (number)

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For the album by George Michael, see Twenty Five (album).
25 20 5

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

Cardinal 25
twenty five
Ordinal 25th
twenty-fifth
Factorization 5^2 \,\!
Divisors 1, 5, 25
Roman numeral XXV
Binary 11001
Hexadecimal 19

Contents

[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.

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 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 xn + 1 = x1,xn + 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.

11:25 is a magic number

[edit] In science

[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:

[edit] In sports

[edit] Historical years

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

Christmas is on the 25th of December