TwentyFive

Twenty-five is the natural number that follows twenty-four and precedes twenty-six. In decimal notation it is written as 25. It can be represented in other bases as binary 11001, hexadecimal 19, and in Roman numerals XXV. It is a perfect square, being 5 squared (5 × 5). Its positive divisors are 1, 5, and 25, making it a composite number that is the product of the same prime factor.

Etymology and linguistic notes: the name twenty-five is a straightforward compound of twenty and five. The word twenty derives from Old English twentig, a form related to other Germanic terms for “ten times two,” while five comes from a much older Proto-Indo-European root. The compound pattern reflects a traditional way of forming numbers in English.

Mathematical properties and significance: as a square number, 25 is the fifth square after 1, 4, 9, and 16. It appears in various mathematical contexts, such as the Pythagorean triple 7-24-25, where 25 is the hypotenuse. In geometry and number theory, 25 often serves as a familiar example due to its simple prime factorization and its role as a square of a small prime.

Cultural and practical usage: the number 25 is commonly used in calendars to denote the 25th day of a month, with December 25 being Christmas Day in many countries. It also marks moments described as “a quarter of a century” or other milestone ages in different cultures. In popular culture, the title 25 has been used prominently, such as in Adele’s 2015 studio album titled 25, which achieved widespread commercial success.

See also: number, square numbers, Roman numerals, calendar dates.