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As a human activity, the practice of mathematics has a social side, which includes education, careers, recognition, popularization, and so on. In education, mathematics is a core part of the curriculum and forms an important element of the STEM academic disciplines.
In some countries, the number 20 is used as an index in measuring visual acuity. 20/20 indicates normal vision at 20 feet, although it is commonly used to mean "perfect vision" in countries using the Imperial system. (The metric equivalent is 6/6.)
The 19th century began on 1 January 1801 (represented by the Roman numerals MDCCCI), and ended on 31 December 1900 (MDCCCXCX). It was the 9th century of the 2nd millennium. It was characterized by vast social upheaval. Slavery was abolished in much of Europe and the Americas.
71 is the 20th prime number. Because both rearrangements of its digits (17 and 71) are prime numbers, 71 is an emirp and more generally a permutable prime. [1] [2] 71 is a centered heptagonal number. [3] It is a Pillai prime, since ! + is divisible by 71, but 71 is not one more than a multiple of 9. [4]
If the number is not already a unit fraction, the first method in this list is to attempt to split the numerator into a sum of divisors of the denominator; this is possible whenever the denominator is a practical number, and Liber Abaci includes tables of expansions of this type for the practical numbers 6, 8, 12, 20, 24, 60, and 100.
[1] RSA Laboratories (which is an initialism of the creators of the technique; Rivest, Shamir and Adleman) published a number of semiprimes with 100 to 617 decimal digits. Cash prizes of varying size, up to US$200,000 (and prizes up to $20,000 awarded), were offered for factorization of some of them. The smallest RSA number was factored in a ...
The home and colonial areas of the world's empires in 1908, as given by The Harmsworth Atlas and Gazetteer. Empire size in this list is defined as the dry land area it controlled at the time, which may differ considerably from the area it claimed.
In Old French (during the Middle Ages), all numbers from 30 to 99 could be said in either base 10 or base 20, e.g. vint et doze (twenty and twelve) for 32, dous vinz et diz (two twenties and ten) for 50, uitante for 80, or nonante for 90. [131] The term octante was historically used in Switzerland for 80, but is now considered archaic. [132]