3 (three) is anumber,numeral anddigit. It is thenatural number following2 and preceding4, and is the smallest oddprime number and the only prime preceding a square number. It has religious and cultural significance in many societies.[1]
The use of three lines to denote the number 3 occurred in many writing systems, including some (like Roman andChinese numerals) that are still in use. That was also the original representation of 3 in theBrahmic (Indian) numerical notation, its earliest forms aligned vertically.[2] However, during theGupta Empire the sign was modified by the addition of a curve on each line. TheNāgarī script rotated the lines clockwise, so they appeared horizontally, and ended each line with a short downward stroke on the right. In cursive script, the three strokes were eventually connected to form a glyph resembling a⟨3⟩ with an additional stroke at the bottom:३.
The Indian digits spread to theCaliphate in the 9th century. The bottom stroke was dropped around the 10th century in the western parts of the Caliphate, such as theMaghreb andAl-Andalus, when a distinct variant ("Western Arabic") of the digit symbols developed, including modern Western 3. In contrast, the Eastern Arabs retained and enlarged that stroke, rotating the digit once more to yield the modern ("Eastern")Arabic digit "٣".[3]
A common graphic variant of the digit three has a flat top, similar to the letterƷ (ezh). This form, sometimes called abanker's 3, can stop a forger from turning the 3 into an 8. It is found onUPC-A barcodes andstandard 52-card decks.[citation needed]
Atriangle is made of threesides. It is the smallest non-self-intersectingpolygon and the only polygon not to have properdiagonals. When doing quick estimates, 3 is a rough approximation ofπ, 3.1415..., and a very rough approximation ofe, 2.71828...
Three is the only prime which is one less than aperfect square. Any other number which is − 1 for some integer is not prime, since it is ( − 1)( + 1). This is true for 3 as well (with = 2), but in this case the smaller factor is 1. If is greater than 2, both − 1 and + 1 are greater than 1 so their product is not prime.
There is some evidence to suggest that early man may have used counting systems which consisted of "One, Two, Three" and thereafter "Many" to describe counting limits. Early peoples had a word to describe the quantities of one, two, and three but any quantity beyond was simply denoted as "Many". This is most likely based on the prevalence of this phenomenon among people in such disparate regions as the deep Amazon and Borneo jungles, where western civilization's explorers have historical records of their first encounters with these indigenous people.[6]
Thetriangle, apolygon with threeedges and threevertices, is the most stable physical shape. For this reason it is widely utilized in construction, engineering and design.[7]
Pythagoras and thePythagorean school highlighted that the number 3, which they calledtriad, is the only number to equal the sum of all the terms below it, and the only number whose sum with those below equals the product of them and itself.[9]
Three (三, formal writing:叁,pinyinsān,Cantonese:saam1) is considered agood number inChinese culture because it sounds like the word "alive" (生 pinyinshēng, Cantonese:saang1), compared tofour (四, pinyin:sì, Cantonese:sei1), which sounds like the word "death" (死 pinyinsǐ, Cantonese:sei2).
The phrase "Third time's the charm" refers to the superstition that after two failures in any endeavor, a third attempt is more likely to succeed.[10] However, some superstitions say the opposite, stating thatluck, especially bad luck, is often said to "come in threes".[11]
One such superstition, called "Three on a Match", says that it is unlucky to be the third person to light a cigarette from the same match or lighter. This superstition is sometimes asserted to have originated among soldiers in the trenches of the First World War when a sniper might see the first light, take aim on the second and fire on the third.[12][13]
^Georges Ifrah,The Universal History of Numbers: From Prehistory to the Invention of the Computer transl. David Bellos et al. London: The Harvill Press (1998): 393, Fig. 24.63
