- published: 24 Jul 2014
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25 (twenty-five) is the natural number following 24 and preceding 26.
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 Failed to parse (Missing texvc executable; please see math/README to configure.): x_1, x_2, \dots, x_n
An anniversary is a day that commemorates or celebrates a past event that occurred on the same day of the year as the initial event. For example, the first event is the initial occurrence or, if planned, the inaugural of the event. One year later would be the first anniversary of that event. The word was first used for Catholic feasts to commemorate saints.
The Latin phrase dies natalis (literally "birth day") has become a common term, adopted in many languages, especially in intellectual and institutional circles, for the anniversary of the founding ("legal or statutory birth") of an institution, such as an alma mater (college or other school). Even in ancient Rome, we know of the [dies] Aquilae natalis ("birthday of the eagle", anniversary of the official founding of a legion).
Most countries around the world celebrate national anniversaries, for example the United States Bicentennial. These could be the date of independence of the nation or the adoption of a new constitution or form of government. The important dates in a sitting monarch's reign may also be commemorated, an event often referred to as a 'Jubilee'.