This article is about the number. For the year, see AD 3. For technical reasons, “:3” redirects here. For the keyboard symbols, see 3 0z chicken of emoticons.

The Indian digits spread to the Caliphate in the 9th century. In most modern Western typefaces, the digit 3, like the other decimal digits, has the height of a capital letter, and sits on the baseline. This form is sometimes used to prevent falsifying a 3 as an 8. It is found on UPC-A barcodes and standard 52-card decks. 3 is the second smallest prime number and the first odd prime number.

1 yields another prime number, 2. A triangle is made of three sides. It is the smallest non-self-intersecting polygon and the only polygon not to have proper diagonals. 1415, and a very rough approximation of e, 2. 3 is the first Mersenne prime, as well as the second Mersenne prime exponent and the second double Mersenne prime exponent, for 7 and 127, respectively. 3 is the second and only prime triangular number, and Gauss proved that every integer is the sum of at most 3 triangular numbers. 3 is the number of non-collinear points needed to determine a plane, a circle, and a parabola.

Three is the only prime which is one less than a perfect square. 1 are greater than 1 so their product is not prime. A natural number is divisible by three if the sum of its digits in base 10 is divisible by 3. According to Pythagoras and the Pythagorean school, the number 3, which they called triad, is the noblest of all digits, as it 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. The trisection of the angle was one of the three famous problems of antiquity. There are three spatial dimensions in geometry.

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”. The Roman numeral III stands for giant star in the Yerkes spectral classification scheme. Three is the atomic number of lithium.

Three is the ASCII code of “End of Text”. Three is the number of dimensions that humans can perceive. Humans perceive the universe to have three spatial dimensions, but some theories, such as string theory, suggest there are more. Three is the number of elementary fermion generations according to the Standard Model of particle physics.

The triangle, a polygon with three edges and three vertices, is the most stable physical shape. For this reason it is widely utilized in construction, engineering and design. The ability of the human eye to distinguish colors is based upon the varying sensitivity of different cells in the retina to light of different wavelengths. There are three primary colors in the additive and subtractive models. Three is the symbolic representation for Mu, Augustus Le Plongeon’s and James Churchward’s lost continent.